Method of manufacturing photoelectric conversion device

ABSTRACT

A fragile layer is formed in a region at a depth of less than 1000 nm from one surface of a single crystal semiconductor substrate, and a first impurity semiconductor layer and a first electrode are formed at the one surface side. After bonding the first electrode and a supporting substrate, the single crystal semiconductor substrate is separated using the fragile layer or the vicinity as a separation plane, thereby forming a first single crystal semiconductor layer over the supporting substrate. An amorphous semiconductor layer is formed on the first single crystal semiconductor layer, and a second single crystal semiconductor layer is formed by heat treatment for solid phase growth of the amorphous semiconductor layer. A second impurity semiconductor layer having a conductivity type opposite to that of the first impurity semiconductor layer and a second electrode are formed over the second single crystal semiconductor layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion deviceincluding a single crystal semiconductor or a polycrystallinesemiconductor and to a manufacturing method of the photoelectricconversion device.

2. Description of the Related Art

The industrial growth has been boosting energy consumption worldwide.The mainly used energy such as oil, coal, and natural gas produces alarge amount of carbon dioxide, which has been a factor of drasticglobal warming in recent years. In response to that, photovoltaic powergeneration which produces less amount of carbon oxide and iseco-friendly is getting popular.

Some photovoltaic power generation utilize solar heat, while many othersemploy photoelectric conversion devices (also called solar cells orphotoelectromotive devices) by which light energy is converted intoelectric energy with use of the photoelectric characteristics ofsemiconductor.

Photoelectric conversion devices are already available in the market andthe production thereof has been expanding year by year with governmentsupport for solar cells around the world. For example, the production ofsolar cells around the world in 2006 is 2521 MW, which has increased byover 40% per annum. Above all, photoelectric conversion devicesincluding a crystalline semiconductor have become popular worldwide, anda large part of the production is occupied by the devices includingsingle crystal silicon substrates or polycrystalline silicon substrates.

As for a crystalline photoelectric conversion device using silicon as amaterial, a thickness of about 10 μm is enough to absorb sunlight.However, a single crystal silicon wafer used in the product has adiameter of 6 inches (150 mm) to 12 inches (300 mm) and a thickness of600 μm to 800 μm, whereas a polycrystalline silicon wafer used in theproduct has a length of 100 mm to 150 mm on each side and a thickness of200 μm to 350 μm. That is to say, the thickness of a single crystalsilicon substrate or a polycrystalline silicon substrate is several tenstimes or more the necessary thickness of a photoelectric conversiondevice and the substrate, which is a material, is not used effectivelyat present. In an extreme case, when a single crystal silicon substrateor a polycrystalline silicon substrate is used in a photoelectricconversion device, most part of the substrate only functions as astructural body that keeps the shape of the photoelectric conversiondevice.

With the increase in production of photoelectric conversion devices yearby year, short of supply and rise of cost of silicon, which is thematerial of single crystal silicon or polycrystalline silicon, havebecome significant problems in the industry. As for the supply-demandbalance of polycrystalline silicon, which had been excess in supplyreflecting semiconductor recession, polycrystalline silicon is now shortof supply since around fiscal 2005 because of drastic expansion of thesolar cell market in addition to the recovery of the semiconductor (LSI)industry. Major silicon suppliers in the world have already tried toincrease capability of silicon production, though the increase in demandoutweighs the capability and the short of supply seems to continue forsome time.

A variety of structures of photoelectric conversion devices have beendisclosed. In addition to a typical structure in which an n type or a ptype diffusion layer is formed in a single crystal silicon substrate ora polycrystalline silicon substrate, a stacked type photoelectricconversion device in which different kinds of unit cells are combinedsuch that a unit cell including a single crystal semiconductor or apolycrystalline semiconductor and a unit cell including an amorphoussemiconductor or a microcrystalline semiconductor are combined is known(e.g., see Patent Document 1: Examined Patent Application PublicationNo. H6-044638). However, the photoelectric conversion device asaforementioned also needs to use a single crystal semiconductorsubstrate or a polycrystalline semiconductor substrate.

In recent years, development has been actively conducted on an SOI(silicon on insulator) structure which includes a single crystal siliconthin film formed over a substrate having an insulating surface. Althoughan SOI substrate is expensive, the cost can be decreased as comparedwith a bulk single crystal silicon substrate as long as an inexpensivesubstrate such as a glass substrate can be used as a supportingsubstrate. Moreover, the consumption of silicon, which is the material,can be decreased. For example, a method of manufacturing an SOIsubstrate in which a single crystal silicon layer is fixed to a glasssubstrate by a hydrogen ion implantation separation method is known(e.g., see Patent Document 2: Japanese Published Patent Application No.H11-097379).

SUMMARY OF THE INVENTION

When a hydrogen ion implantation separation method is employed, a singlecrystal silicon thin film which is homogeneous can be formed through alow-temperature process as compared with when a SIMOX substrate or abonding substrate utilizing grinding or polishing is used. Furthermore,a single crystal silicon substrate from which a single crystal siliconthin film has been separated can be reused, which can achieve effectiveutilization of resources.

In the case of manufacturing a photoelectric conversion device with useof an SOI substrate, a single crystal silicon thin film needs to havelarge thickness to some extent in order to effectively absorb sunlight.As for solar cells, a single crystal silicon thin film with a thicknessof at least 800 nm is necessary in consideration of photoelectricconversion efficiency. In the case of employing a hydrogen ionimplantation separation method, the depth of ion implantation in asingle crystal silicon substrate is determined depending on theacceleration voltage of an ion implantation apparatus. Based on thedepth of ion implantation, the film thickness of a single crystalsilicon thin film is determined. However, the acceleration voltage of anion implantation apparatus has limitation in terms of the apparatus, sothat there is the upper limit of the depth of ion implantation in asingle crystal silicon substrate. Moreover, in order to increase thedepth of ion implantation, it is necessary to increase the accelerationvoltage at the time of ion implantation. However, it was difficult for aconventional apparatus to give a large amount of current by increasingthe acceleration voltage. Therefore, when the acceleration voltage isincreased, a long period of time is necessary in order to obtain a givenimplantation amount, which results in that the cycle time mightdecrease.

In view of the aforementioned problems, it is an object of the presentinvention to provide a photoelectric conversion device having anexcellent photoelectric conversion characteristic and its manufacturingmethod, while effectively utilizing limited resources.

Utilizing a crystal solid phase growth technique, a single crystalsemiconductor layer that forms a photoelectric conversion layer is madethick. Utilizing a bonding technique of different kinds of substrates, asingle crystal semiconductor layer is formed over a supportingsubstrate. The single crystal semiconductor layer is obtained by slicinga single crystal semiconductor substrate. An amorphous semiconductorlayer is formed on the single crystal semiconductor layer fixed to thesupporting substrate and heat treatment is performed. The single crystalsemiconductor layer that is in contact with the amorphous semiconductorlayer serves as a seed crystal, and the amorphous semiconductor layer issubjected to solid phase growth, whereby single crystallization isperformed. That is, the amorphous semiconductor layer becomes a singlecrystal semiconductor layer, and as a result, the single crystalsemiconductor layer is made thick. By solid phase growth of theamorphous semiconductor layer, the single crystal semiconductor layercan be easily made thick.

In an aspect of a method of manufacturing a photoelectric conversiondevice according to the present invention, a fragile layer is formed ina region at a depth of less than 1000 nm from one surface of a singlecrystal semiconductor substrate, and a first impurity semiconductorlayer and a first electrode are formed on the one surface side of thesingle crystal semiconductor substrate. After bonding the firstelectrode and a supporting substrate to each other, the single crystalsemiconductor substrate is separated using the fragile layer or thevicinity of the fragile layer as a separation plane, thereby forming afirst single crystal semiconductor layer over the supporting substrate.An amorphous semiconductor layer is formed on a separation plane of thefirst single crystal semiconductor layer, and heat treatment for solidphase growth of the amorphous semiconductor layer is performed to form asecond single crystal semiconductor layer. A second impuritysemiconductor layer having a conductivity type opposite to that of thefirst impurity semiconductor layer is formed over the second singlecrystal semiconductor layer, and a second electrode is formed over thesecond impurity semiconductor layer.

Note that “cleavage” in this specification refers to separation of asingle crystal semiconductor substrate at a fragile layer or thevicinity of the fragile layer. Further, “separation plane” refers to aplane formed by separating a single crystal semiconductor substrate at afragile layer or the vicinity of the fragile layer.

In an aspect of a method of manufacturing a photoelectric conversiondevice according to the present invention, a fragile layer is formed ina region at a depth of less than 1000 nm from one surface of a singlecrystal semiconductor substrate, and a first impurity semiconductorlayer and a first electrode are formed on the one surface side of thesingle crystal semiconductor substrate. After bonding the firstelectrode and a supporting substrate to each other, the single crystalsemiconductor substrate is separated using the fragile layer or thevicinity of the fragile layer as a separation plane, thereby forming afirst single crystal semiconductor layer over the supporting substrate.An amorphous semiconductor layer is formed on a separation plane of thefirst single crystal semiconductor layer and an amorphous semiconductorlayer having a conductivity type opposite to that of the first impuritysemiconductor layer is formed on the amorphous semiconductor layer, andthen heat treatment for solid phase growth of the amorphoussemiconductor layer and the amorphous semiconductor layer having aconductivity type is performed to form a second single crystalsemiconductor layer and a second impurity semiconductor layer; and asecond electrode is formed over the second impurity semiconductor layer.

In any of the above structures, an insulating layer can be formed overthe first electrode before bonding with the supporting substrate, sothat the first electrode and the supporting substrate are bonded withthe insulating layer interposed therebetween.

In any of the above structures, the fragile layer preferably containsions or cluster ions generated from a source gas containing hydrogen andis preferably formed by irradiating the single crystal semiconductorsubstrate with ions which are accelerated by voltage without massseparation. Further, the proportion of H₃ ⁺ ions with respect to thetotal amount of the ions or cluster ions to be irradiated is preferablylarge.

In any of the above structures, the total thickness of the first singlecrystal semiconductor layer and the second single crystal semiconductorlayer is preferably 800 nm or more.

In any of the above structures, the first single crystal semiconductorlayer can be formed to be of p type by using a p type single crystalsemiconductor substrate as the single crystal semiconductor substrate,while the second single crystal semiconductor layer can be formed to beintrinsic by using an intrinsic semiconductor as the amorphoussemiconductor layer. Moreover, the first impurity semiconductor layercan be of p type while the second impurity semiconductor layer can be ofn type.

Note that an “intrinsic semiconductor (i type semiconductor)” in thisspecification refers to a semiconductor which is intrinsic orsubstantially intrinsic, and indicates a semiconductor which has animpurity element imparting one conductivity type (an impurity elementimparting p type conductivity or n type conductivity) at a concentrationof 1×10²⁰/cm³ or less and oxygen and nitrogen each at a concentration of9×10¹⁹/cm³ or less and which has photoconductivity of 100 times or morethe dark conductivity. An intrinsic semiconductor may contain boron at 1ppm to 1000 ppm. An intrinsic semiconductor sometimes has weak n typeconductivity when an impurity element for controlling valence electronsis not added intentionally. Therefore, an impurity element imparting ptype conductivity is added at the same time as or after the filmformation, in some cases. The impurity element imparting p typeconductivity is typically boron, and an impurity gas such as B₂H₆, BF₃,or the like may be mixed into a semiconductor material gas at a ratio of1 ppm to 1000 ppm. The concentration of boron may be, for example,1×10¹⁴/cm³ to 6×10¹⁶/cm³.

Since the thickness of the single crystal semiconductor layer forforming the photoelectric conversion layer is increased in accordancewith a crystal solid phase growth technique, it is possible to improvephotoelectric conversion efficiency while suppressing the consumption ofresources. Moreover, the consumption of a single crystal semiconductor,which is the material, can be reduced by slicing a superficial portionof a single crystal semiconductor substrate and bonding the portion tothe supporting substrate as a single crystal semiconductor layer.Furthermore, the single crystal semiconductor substrate from which thesingle crystal semiconductor layer has been separated can be reused.Thus, the resources can be effectively utilized and a photoelectricconversion device having an excellent photoelectric conversioncharacteristic can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of aphotoelectric conversion device according to an aspect of the presentinvention.

FIG. 2 is a top view illustrating an example of a photoelectricconversion device according to an aspect of the present invention.

FIGS. 3A to 3D are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 4A and 4B are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 5A to 5C are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 6A and 6B are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

Part (A) of FIG. 7 is a cross-sectional view of a unit cell of aphotoelectric conversion device according to an aspect of the presentinvention and Part (B) of FIG. 7 is an energy band diagram correspondingto Part (A) of FIG. 7.

FIG. 8 is a cross-sectional view illustrating an example of aphotoelectric conversion device according to an aspect of the presentinvention.

FIGS. 9A to 9C each illustrate a mode of a semiconductor substrate witha given shape cut out from a circular single crystal semiconductorsubstrate.

FIGS. 10A to 10D are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 11A to 11D are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 12A to 12D are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIGS. 13A and 13B are cross-sectional views illustrating an example of amethod of manufacturing a photoelectric conversion device according toan aspect of the present invention.

FIG. 14 is a cross-sectional view illustrating an example of a tandemphotoelectric conversion device according to an aspect of the presentinvention.

FIGS. 15A and 15B are cross-sectional views illustrating an example of amethod of manufacturing a tandem photoelectric conversion deviceaccording to an aspect of the present invention.

FIGS. 16A and 16B are cross-sectional views illustrating an example of amethod of manufacturing a tandem photoelectric conversion deviceaccording to an aspect of the present invention.

Part (A) of FIG. 17 is a cross-sectional view of a unit cell of aphotoelectric conversion device according to an aspect of the presentinvention and Part (B) of FIG. 17 is an energy band diagramcorresponding to Part (B) of FIG. 17.

FIG. 18 is a cross-sectional view illustrating an example of a stackedphotoelectric conversion device according to an aspect of the presentinvention.

Part (A) of FIG. 19 is a cross-sectional view of a unit cell of astacked photoelectric conversion device according to an aspect of thepresent invention and Part (B) of FIG. 19 is an energy band diagramcorresponding to Part (A) of FIG. 19.

FIG. 20 is a cross-sectional view illustrating an example of a method ofmanufacturing a photoelectric conversion device according to an aspectof the present invention.

FIG. 21 is a schematic diagram illustrating a structure of a laserprocessing apparatus which can be applied to the present invention.

FIG. 22 is a schematic diagram illustrating a structure of an ion dopingapparatus which can be applied to the present invention.

FIG. 23 is a cross-sectional view illustrating an example of aphotoelectric conversion device according to an aspect of the presentinvention.

FIGS. 24A and 24B are schematic diagrams for illustrating a structure ofa photovoltaic power generation module.

FIG. 25 is a schematic diagram for illustrating an example of aphotovoltaic power generation system.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

Embodiment Modes of the present invention are hereinafter described indetail with reference to the drawings. However, it is to be easilyunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the invention, they should beconstrued as being included therein. Note that in the structure of thepresent invention which is hereinafter described, the reference numeralsdenoting the same portions are used in common in different drawings.

Embodiment Mode 1

FIG. 1 is a schematic cross-sectional view of a photoelectric conversiondevice 100 according to this embodiment mode. FIG. 2 is a schematic topview of the photoelectric conversion device 100 according to thisembodiment mode. Note that FIG. 1 illustrates an example of across-sectional view along a line O-P in FIG. 2.

The photoelectric conversion device 100 described in this embodimentmode includes a unit cell 120 fixed to a supporting substrate 102. Theunit cell 120 includes a single crystal semiconductor layer. The unitcell 120 is provided with a first electrode 106 on the supportingsubstrate 102 side and with a second electrode 118 on the surface sideof the unit cell 120. Moreover, an auxiliary electrode 116 is providedin electrical connection with the first electrode 106. The photoelectricconversion device 100 of this embodiment mode has a structure in whichthe unit cell 120 is fixed to the supporting substrate 102, and apositive electrode and a negative electrode, or electrodes eachconnected to a positive or negative electrode are exposed to the samesurface side of the supporting substrate 102.

The supporting substrate 102 to which the unit cell 120 is fixed is asubstrate having an insulating surface or an insulating substrate, andany of a variety of glass substrates that are used in the electronicsindustry, such as aluminosilicate glass substrates, aluminoborosilicateglass substrates, and barium borosilicate glass substrates, can be used.

An insulating layer 104 is provided between the supporting substrate 102and the unit cell 120. The first electrode 106 is provided between theunit cell 120 and the insulating layer 104, and the second electrode 118is provided on a surface of the unit cell 120 on the side opposite tothe supporting substrate 102 side. The unit cell 120 is sandwichedbetween the first electrode 106 and the second electrode 118. Moreover,the insulating layer 104 is bonded to the supporting substrate 102 andfurther in close contact with the first electrode 106, whereby the unitcell 120 is fixed to the supporting substrate 102. That is to say, theinsulating layer 104 functions as a bonding layer that bonds the unitcell 120 and the supporting substrate 102 to each other. For example, alayer with an average surface roughness Ra of 0.5 nm or less, preferably0.3 nm or less is formed as the insulating layer 104. Note that theaverage surface roughness (Ra) in this specification refers tocenterline average roughness defined according to JIS B0601 which isexpanded three dimensionally so as to correspond to a plane.

The first electrode 106 is provided between the unit cell 120 and thesupporting substrate 102. The unit cell 120 is provided over theapproximately entire surface of the first electrode 106 and thesupporting substrate 102 is provided under the first electrode 106.Therefore, in this state, electric energy is difficult to extract fromthe photoelectric conversion device to the outside. Accordingly, theauxiliary electrode 116 for electric connection is formed as anextracting electrode, so that electric energy can be easily extracted tothe outside.

The unit cell 120 has a stacked structure in which a first impuritysemiconductor layer 108 having one conductivity type, a first singlecrystal semiconductor layer 110, a second single crystal semiconductorlayer 112, and a second impurity semiconductor layer 114 having aconductivity type opposite to that of the first impurity semiconductorlayer 108 are sequentially stacked. Note that the first impuritysemiconductor layer 108 may be omitted if the second impuritysemiconductor layer 114 and the first single crystal semiconductor layer110 have the opposite conductivity type to each other.

Single crystal silicon is used typically for the first single crystalsemiconductor layer 110 and the second single crystal semiconductorlayer 112 of the unit cell 120. Moreover, a polycrystallinesemiconductor layer (typically, polycrystalline silicon) may be usedinstead of the single crystal semiconductor layer. Each of the firstimpurity semiconductor layer 108 having one conductivity type and thesecond impurity semiconductor layer 114 having a conductivity typeopposite to that of the first impurity semiconductor layer 108corresponds to a semiconductor layer to which an impurity elementimparting a given conductivity type has been added. If the firstimpurity semiconductor layer 108 is of p type, the second impuritysemiconductor layer 114 is of n type. Needless to say, the firstimpurity semiconductor layer 108 may be of n type and the secondimpurity semiconductor layer 114 may be of p type. An element belongingto Group 13 of the periodic table, such as boron or aluminum, is used asa p type impurity element, and an element belonging to Group 15 of theperiodic table, such as phosphorus or arsenic, is used as an n typeimpurity element. The impurity element can be added by ion implantationor ion doping.

In this specification, “ion implantation” refers to a method by whichions generated from a source gas are mass separated and introduced to anobject, while “ion doping” refers to a method by which ions generatedfrom a source gas are introduced to an object without mass separation.

The first single crystal semiconductor layer 110 is formed by slicing asingle crystal semiconductor substrate. For example, ions or clusterions generated from a source gas containing hydrogen are introduced athigh concentration at a given depth of a single crystal semiconductorsubstrate, and then heat treatment is performed thereon. Thus, a singlecrystal semiconductor layer at a superficial layer can be separated.Alternatively, a single crystal semiconductor layer may be epitaxiallygrown on a porous semiconductor layer (typically, a porous siliconlayer) and then the porous semiconductor layer may be cleaved to beseparated by water-jetting. As the single-crystal semiconductorsubstrate, a single crystal silicon wafer is typically employed.

The second single crystal semiconductor layer 112 is formed by solidphase growth (solid phase epitaxy (SPE)) of an amorphous semiconductorlayer. Specifically, an amorphous semiconductor layer is formed on thefirst single crystal semiconductor layer 110, and then heat treatment isperformed. Thus, the first single crystal semiconductor layer 110 isused as a seed crystal to perform solid phase growth and singlecrystallization, whereby the second single crystal semiconductor layer112 can be formed.

The single crystal semiconductor layer which forms the photoelectricconversion layer of the unit cell 120 includes the first single crystalsemiconductor layer 110 and the second single crystal semiconductorlayer 112 and has a total film thickness of 800 nm or more, preferably1000 nm or more. The first single crystal semiconductor layer 110 whichserves as a seed crystal has a thickness of less than 1000 nm,preferably less than 800 nm, and more preferably greater than or equalto 5 nm and less than or equal to 300 nm. An amorphous semiconductorlayer is formed on the first single crystal semiconductor layer 110, andsolid phase growth and single crystallization are performed by heattreatment. Although the amorphous semiconductor layer may be formed by aCVD method typified by a plasma CVD method, a sputtering method, or thelike, in consideration of cycle time for film formation or the like, itis preferable that the film thickness is greater than or equal to 100 nmand less than or equal to 2000 nm. If single crystal silicon is used forthe first single crystal semiconductor layer 110 and the second singlecrystal semiconductor layer 112, a thickness of at least about 800 nm isnecessary to absorb sunlight because single crystal silicon has anenergy gap of 1.12 eV and is an indirect transition type semiconductor.

Note that single crystals are crystals which have uniform crystal planesand uniform crystal axes, and atoms or molecules that form the singlecrystals are spatially ordered. However, although single crystals arestructured by orderly aligned atoms, single crystals may include alattice defect in which the alignment is disordered as part or singlecrystals may include intended or unintended lattice strain.

In this specification, a CVD method (also referred to as a chemicalvapor deposition method) includes a plasma CVD method, a photo CVDmethod, and a thermal CVD method in its category, and the thermal CVDmethod includes a low pressure CVD method and an atmospheric pressureCVD method in its category.

The first single crystal semiconductor layer 110 and the second singlecrystal semiconductor layer 112 each are a single crystal of the samesemiconductor material and a single crystal semiconductor of the samematerial. Therefore, the first single crystal semiconductor layer 110and the second single crystal semiconductor layer 112 have asubstantially uniform crystal plane and a substantially uniform crystalaxis (crystal orientation).

However, the first single crystal semiconductor layer 110 and the secondsingle crystal semiconductor layer 112 have different conductivity typesin some cases. If the first single crystal semiconductor layer 110 isformed by slicing a p type single crystal semiconductor substrate, thefirst single crystal semiconductor layer 110 is of p type. If the firstsingle crystal semiconductor layer 110 is formed by slicing an n typesingle crystal semiconductor substrate, the first single crystalsemiconductor layer 110 is of n type. The second single crystalsemiconductor layer 112 is an intrinsic (i type) semiconductor whensolid phase growth of a substantially intrinsic amorphous semiconductorlayer is performed. In addition, the second single crystal semiconductorlayer 112 is a weak n type (referred to as n-type) in some cases when anamorphous semiconductor layer before solid phase growth contains a largeamount of impurities such as oxygen or the like.

The crystallinity of the second single crystal semiconductor layer 112can be known based on peak positions of Raman shift obtained frommeasurement data of Raman spectrum, inverse pole figure (IPF) map ofelectron beams obtained from measurement data of electron backscatterdiffraction pattern (EBSP), lattice images or electron beam diffractionimages obtained from a transmission electron microscope (TEM), and thelike.

The second electrode 118 has a grid shape (or a comb-like shape or apectinate shape) so that the effective area for light to enter the unitcell 120 is as large as possible. In the photoelectric conversion deviceaccording to this embodiment mode, the area of the second electrode 118that covers the surface of the unit cell 120 is made as small aspossible so that the surface of the unit cell 120 is exposed as large aspossible, because light is absorbed from the second electrode 118 side.

Further, the auxiliary electrode 116 is provided in electricalconnection with the first electrode 106. The auxiliary electrode 116 andthe second electrode 118 are exposed to the same surface side.

Next, an example of a method of manufacturing the photoelectricconversion device 100 of this embodiment mode is described withreference to FIGS. 3A to 3D, FIGS. 4A and 4B, FIGS. 5A to 5C, and FIGS.6A and 6B.

A single crystal semiconductor substrate 103 is prepared. A fragilelayer 105 is formed in a region at a given depth of the single crystalsemiconductor substrate 103, and the first impurity semiconductor layer108 is formed on one surface side of the single crystal semiconductorsubstrate 103. Moreover, the first electrode 106 and the insulatinglayer 104 are sequentially stacked over the one surface of the singlecrystal semiconductor substrate 103. Note that the first electrode 106is formed on the side where the first impurity semiconductor layer 108was formed or on one surface side where the first impurity semiconductorlayer 108 will be formed (see FIG. 3D).

The order of forming the fragile layer 105, the first impuritysemiconductor layer 108, the first electrode 106, and the insulatinglayer 104 is not limited; they may be formed in accordance with any ofthe following (1) to (4). (1) A protection layer is formed on onesurface of a single crystal semiconductor substrate, a first impuritysemiconductor layer is formed at the one surface side of the singlecrystal semiconductor substrate by adding an impurity element impartingone conductivity type through the surface where the protection layer isformed, and a fragile layer is formed in a region at a given depth ofthe single crystal semiconductor substrate by irradiating the singlecrystal semiconductor substrate with ions or cluster ions through thesurface where the protection layer is formed. After removing theprotection layer, a first electrode is formed over the first impuritysemiconductor layer on the surface side where the protection layer wasformed and then an insulating layer is formed over the first electrode.(2) A protection layer is formed on one surface of a single crystalsemiconductor substrate, a fragile layer is formed in a region at agiven depth of the single crystal semiconductor substrate by irradiatingthe single crystal semiconductor substrate with ions or cluster ionsthrough the surface where the protection layer is formed, and a firstimpurity semiconductor layer is formed at the one surface side of thesingle crystal semiconductor substrate by adding an impurity elementimparting one conductivity type through the surface where the protectionlayer is formed. After removing the protection layer, a first electrodeis formed over the first impurity semiconductor layer on the surfaceside where the protection layer was formed, and then an insulating layeris formed over the first electrode. (3) A first electrode is formed onone surface of a single crystal semiconductor substrate. An impurityelement imparting one conductivity type is added through the surfacewhere the first electrode is formed, whereby a first impuritysemiconductor layer is formed at the one surface side of the singlecrystal semiconductor substrate where the first electrode is formed.Further, a fragile layer is formed in a region at a given depth of thesingle crystal semiconductor substrate by irradiating the single crystalsemiconductor substrate with ions or cluster ions through the surfacewhere the first electrode is formed, and then an insulating layer isformed over the first electrode. (4) A first electrode is formed on onesurface of a single crystal semiconductor substrate. A fragile layer isformed in a region at a given depth of the single crystal semiconductorsubstrate by irradiating the single crystal semiconductor substrate withions or cluster ions through the surface where the first electrode isformed. An impurity element imparting one conductivity type is addedthrough the surface where the first electrode is formed, whereby a firstimpurity semiconductor layer is formed at the one surface side of thesingle crystal semiconductor substrate where the first electrode isformed. An insulating layer is formed over the first electrode.

In this embodiment mode, the example whose formation order follows (1)is described with reference to FIGS. 3A to 3D.

A protection layer 107 is formed on one surface of the single crystalsemiconductor substrate 103. Then, the first impurity semiconductorlayer 108 is formed by adding an impurity element imparting oneconductivity type through the surface where the protection layer 107 isformed (see FIG. 3A).

As the single crystal semiconductor substrate 103, a semiconductor waferof silicon, germanium, or the like; a compound semiconductor wafer ofgallium arsenide, indium phosphide, or the like; or the like is used. Asingle crystal silicon wafer is preferably used. The shape of a top faceof the single crystal semiconductor substrate 103 is not particularlylimited but is preferably substantially quadrilateral if a supportingsubstrate to which the single crystal semiconductor substrate 103 islater fixed is rectangular in shape. Moreover, the surface of the singlecrystal semiconductor substrate 103 is preferably polished to have amirror surface considering that the substrate is later fixed to thesupporting substrate. For example, a p type single crystal silicon waferwith a resistivity of about 1 Ωcm to 10 Ωcm is used as the singlecrystal semiconductor substrate 103.

Many of single crystal silicon wafers circulating in the market arecircular in shape. In those cases, a circular single crystal siliconwafer may be cut into a substantially quadrilateral shape. For example,a circular single crystal semiconductor substrate 101 as illustrated inFIG. 9A can be cut into a single crystal semiconductor substrate 103 awith a substantially quadrilateral shape as illustrated in FIG. 9B or asingle crystal semiconductor substrate 103 b with a substantiallyquadrilateral shape as illustrated in FIG. 9C. Note that FIG. 9Billustrates the case where the single crystal semiconductor substrate103 a is cut out to have a quadrilateral shape of maximum size with itscorners being in contact with the periphery of the circular singlecrystal semiconductor substrate 101. The angle at each corner of thesingle crystal semiconductor substrate 103 a is about 90 degrees. FIG.9C illustrates the case where the single crystal semiconductor substrate103 b is cut out so that the distance between the opposing lines islonger than that of the rectangular region with the maximum size whosecorners are in contact with the periphery of the circular single crystalsemiconductor substrate 101. The angle at each corner of the singlecrystal semiconductor substrate 103 b is not 90 degrees, and the singlecrystal semiconductor substrate 103 b has a polygonal shape, not arectangular shape.

As illustrated in FIG. 3A, the protection layer 107 is formed on onesurface of the single crystal semiconductor substrate 103. Theprotection layer 107 is preferably formed of silicon oxide or siliconnitride specifically by a plasma CVD method. Alternatively, theprotection layer 107 can be formed by oxidizing the single crystalsemiconductor substrate 103 with use of oxidizing chemicals or oxygenradicals. Further alternatively, the protection layer 107 can be formedby oxidizing the surface of the single crystal semiconductor substrate103 by a thermal oxidation method. By the formation of the protectionlayer 107, it is possible to prevent the substrate surface from beingdamaged at the time of forming the fragile layer in the single crystalsemiconductor substrate 103 or adding an impurity element imparting oneconductivity type to the single crystal semiconductor substrate.

An impurity element imparting one conductivity type is added to thesingle crystal semiconductor substrate 103, whereby the first impuritysemiconductor layer 108 is formed at the one surface side of the singlecrystal semiconductor substrate 103. The first impurity semiconductorlayer 108 is formed to a thickness of 30 nm to 150 nm, preferably 50 nmto 100 nm. The impurity element imparting one conductivity type is addedthrough the protection layer 107 formed over the single crystalsemiconductor substrate 103. For example, boron is added as the impurityelement imparting one conductivity type, thereby forming the p typefirst impurity semiconductor layer 108. Boron is added preferably usingan ion doping apparatus in such a manner that ions generated from asource gas containing B₂H₆ or BF₃ are accelerated by voltage withoutmass separation and the substrate is irradiated with the ions. This isbecause the area to be irradiated with the ion beam can be enlarged evenwhen the area of the single crystal semiconductor substrate 103 exceeds300 mm diagonally, and the process can be efficient. For example, alinear ion beam whose long side has a length of more than 300 mm isformed and delivered from one end to the other end of the single crystalsemiconductor substrate 103; thus, the first impurity semiconductorlayer 108 can be formed homogeneously over the entire surface of thesingle crystal semiconductor substrate 103.

The first impurity semiconductor layer 108 can be formed by a thermaldiffusion method. However, a thermal diffusion method is carried outbefore the formation of the fragile layer because a high temperature ofabout 900° C. or more is applied.

In the photoelectric conversion device of this embodiment mode, thefirst impurity semiconductor layer 108 is disposed on the side oppositeto the light incidence side so that a back surface field (BSF) isformed. If the single crystal semiconductor substrate 103 is a p typesubstrate, the impurity semiconductor layer containing a p type impurityelement (the first impurity semiconductor layer 108 in this embodimentmode) is not necessary. However, by arrangement of a high-concentrationp type region (the first impurity semiconductor layer 108) and alow-concentration p type region (the first single crystal semiconductorlayer sliced from the single crystal semiconductor substrate) in thismanner, light confinement effect can prevent recombination of carriers(electrons and holes) generated by light excitation and increase carriercollecting efficiency. Accordingly, the photoelectric conversionefficiency of the photoelectric conversion device can be improved.

The single crystal semiconductor substrate 103 is irradiated with ionsor cluster ions generated from a source gas containing hydrogen, therebyforming the fragile layer 105 in a region at a given depth of the singlecrystal semiconductor substrate 103 (see FIG. 3B). By the irradiationwith the ions or cluster ions, hydrogen is introduced to the singlecrystal semiconductor substrate 103, whereby Si—Si bonds aredisconnected and terminated with hydrogen in a region of the singlecrystal semiconductor substrate 103 where hydrogen is introduced.Therefore, the fragile layer 105 is formed at a certain depth of thesingle crystal semiconductor substrate 103, and the depth is inproportion to the acceleration voltage.

The single crystal semiconductor substrate 103 is irradiated with theions or cluster ions through the surface where the protection layer 107is formed, and the fragile layer 105 is formed in a region at a certaindepth from the surface of the single crystal semiconductor substrate103. As the ions or cluster ions generated from the source gascontaining hydrogen, H⁺ ions, H₂ ³⁰ ions, and H₃ ⁺ ions are given. H₃ ⁺ions are preferably used because the introduction efficiency of hydrogencan be improved to shorten the cycle time of forming the fragile layer105. The depth of the fragile layer 105 in the single crystalsemiconductor substrate 103 is controlled by the acceleration voltage atthe time of ion introduction. Moreover, the thickness of the singlecrystal semiconductor layer to be separated from the single crystalsemiconductor substrate 103 depends on the depth at which the fragilelayer 105 is formed. Accordingly, the acceleration voltage of the ionsis determined in consideration of the thickness of the single crystalsemiconductor layer to be separated.

The depth at which the fragile layer 105 is formed is less than 1000 nm,preferably less than 800 nm, and more preferably greater than or equalto 5 nm and less than or equal to 300 nm from the surface of the singlecrystal semiconductor substrate 103. The shallower the fragile layer 105is formed, the thicker the single crystal semiconductor substrateremains after the separation of the single crystal semiconductor layer;accordingly, the number of times of reusing the substrate can beincreased. However, the acceleration voltage needs to be lower in orderto form the fragile layer 105 shallower. When the acceleration voltageis low, the introduction takes longer time and the cycle time goesworse; therefore, the fragile layer 105 is formed at a depth inconsideration of the productivity or the like.

The doping with the cluster ions such as H₃ ⁺ ions can be performedusing an ion doping apparatus in such a manner that hydrogen plasma isgenerated from a source gas containing hydrogen, the cluster ionsgenerated in the hydrogen plasma are accelerated by voltage without massseparation, and introduction is performed. By the use of the ion dopingapparatus, the single crystal semiconductor substrate 103 even with alarge area can be homogeneously doped.

Here, an example of forming the fragile layer 105 is described. Forexample, a single crystal silicon substrate is used as the singlecrystal semiconductor substrate 103 and the protection layer 107 isformed to a thickness of 100 nm. Ion doping is performed under thecondition where H₂ is used for a source gas, the acceleration voltage is25 kV, the RF electric power is 100 W, and the dosage is 2.2×10¹⁶ions/cm². With the fragile layer 105 formed under such a condition, asingle crystal silicon layer of about 120 nm thick can be separated fromthe single crystal silicon substrate by later heat treatment.

FIG. 22 illustrates an example of a schematic diagram, which describes astructure of an ion doping apparatus that irradiates the single crystalsemiconductor substrate 103 with a plurality of kinds of ions generatedfrom an ion source 2000 without mass separation. A given source gascontaining hydrogen or the like is supplied from a gas supply portion2004 to the ion source 2000. The ion source 2000 is provided withfilaments 2001. A filament power source 2002 applies arc dischargevoltage to each filament 2001 to control the amount of current thatflows to the filament 2001. The source gas supplied from the gas supplyportion 2004 is exhausted from an exhaustion system.

The ions generated from the ion source 2000 are extracted through anextraction electrode system 2005, and an ion beam 2017 is thus formed.The single crystal semiconductor substrate 103 disposed on a mountingboard 2006 is irradiated with the ion beam 2017. The proportions of thekinds of ions in the ion beam 2017 are calculated with a massspectrometer tube 2007 provided in the vicinity of the mounting board2006. The ion density calculated with the mass spectrometer tube 2007 isconverted into signals by using a mass spectrometer 2008 and the resultsmay be fed back to a power source controller 2003. The power sourcecontroller 2003 can control the filament power sources 2002 inaccordance with calculation results on the ion density.

As illustrated in FIG. 22, the source gas containing hydrogen or thelike supplied from the gas supply portion 2004 flows through the chamberof the ion doping apparatus and is exhausted through the exhaustionsystem.

The irradiation of the substrate with the ion beam containing a largeamount of H₃ ⁺ ions, which are cluster ions, gives advantageous effectsin that the introduction efficiency of hydrogen is improved and hydrogencan be introduced to the single crystal semiconductor substrate 103 athigh concentration even if the dosage is low, as compared with theirradiation with H⁺ ions or H₂ ⁺ ions.

When the proportion of H₃ ⁺ ions is high, the fragile layer 105 cancontain hydrogen at a concentration of 1×10²⁰ atoms/cm³ or more,preferably 5×10²⁰ atoms/cm³ or more. Since the region containinghydrogen at high concentration is formed locally in the single crystalsemiconductor substrate 103, a crystal structure is damaged andmicrovoids are formed. Therefore, the fragile layer 105 formed in thesingle crystal semiconductor substrate 103 has a porous structure. Whenheat treatment is performed at comparatively low temperature (600° C. orlower), the microvoids formed in the fragile layer 105 change in volume,whereby the single crystal semiconductor substrate 103 can be cleavedalong the fragile layer 105. The concentration of hydrogen in thefragile layer 105 depends on the dosage, acceleration voltage, or thelike of the ions or cluster ions.

Note that the depth at which the fragile layer 105 is formed can behomogenized when the ions or cluster ions are introduced in such amanner that a linear ion beam longer than one side of the single crystalsemiconductor substrate 103 with a substantially quadrilateral shapescans the surface of the single crystal semiconductor substrate 103.

Moreover, when the fragile layer 105 is formed in such a manner that thesubstrate is irradiated through the first impurity semiconductor layer108 with the ions or cluster ions generated from a source gas containinghydrogen, hydrogenation of the first impurity semiconductor layer 108can also be performed at the same time.

After the protection layer 107 formed over the single crystalsemiconductor substrate 103 is removed, the first electrode 106 isformed over the first impurity semiconductor layer 108 (see FIG. 3C).

The first electrode 106 needs to be formed of a material which resiststhe temperature of heat treatment later performed for separating thesingle crystal semiconductor substrate 103; therefore, a metal with ahigh melting point is preferred. Specifically, the heat resistance tothe temperature about the strain point of the supporting substrate 102is necessary. For example, a metal material such as titanium,molybdenum, tungsten, tantalum, chromium, or nickel is applied. Astacked structure of the aforementioned metal material and nitride ofthe metal material can be applied. For example, a stacked structure of atitanium nitride layer and a titanium layer, a stacked structure of atantalum nitride layer and a tantalum layer, a stacked structure of atungsten nitride layer and a tungsten layer, and the like are given. Inthe case of the stacked structure containing nitride, the nitride isformed in contact with the first impurity semiconductor layer 108. Bythe formation of the nitride, the first electrode 106 and the firstimpurity semiconductor layer 108 can have closer contact to each other.The first electrode 106 is formed by an evaporation method or asputtering method.

The insulating layer 104 is formed over the first electrode 106 (seeFIG. 3D). The insulating layer 104 may have a single-layer structure ora stacked structure of two or more layers; in any case, the outermostsurface (bonding plane) of the insulating layer 104 is preferablysmooth. In addition to being smooth, the outermost surface is morepreferably hydrophilic. For example, a silicon oxide layer, a siliconnitride layer, a silicon oxynitride layer, or a silicon nitride oxidelayer is formed. As a method of forming the insulating layer 104, a CVDmethod is preferred. In particular, a layer with excellent smoothnesscan be formed by a plasma CVD method. As for the smoothness of theinsulating layer 104, specifically, the average surface roughness Ra is0.5 nm or less, preferably 0.3 nm or less.

Note that a silicon oxynitride layer in this specification means a layerthat contains more oxygen than nitrogen, and in the case wheremeasurements are performed using Rutherford backscattering spectrometry(RBS) and hydrogen forward scattering (HFS), contains oxygen, nitrogen,silicon, and hydrogen at concentrations ranging from 50 at. % to 70 at.%, 0.5 at. % to 15 at. %, 25 at. % to 35 at. %, and 0.1 at. % to 10 at.%, respectively. Further, a silicon nitride oxide layer means a layerthat contains more nitrogen than oxygen and, in the case wheremeasurements are performed using RBS and HFS, contains oxygen, nitrogen,silicon, and hydrogen at concentrations ranging from 5 at. % to 30 at.%, 20 at. % to 55 at. %, 25 at. % to 35 at. %, and 10 at. % to 30 at. %,respectively.

As the layer having a smooth and hydrophilic surface, for example,silicon oxide formed by a CVD method using organosilane for a source gasis preferably used. For instance, the bonding between the supportingsubstrate and the unit cell to be formed later can be strengthened if asilicon oxide layer formed by a plasma CVD method using organosilane fora source gas is used. Examples of organosilane that can be used includesilicon-containing compounds such as tetraethoxysilane (TEOS) (chemicalformula: Si(OC₂H₅)₄), tetramethylsilane (TMS) (chemical formula:Si(CH₃)₄), tetramethylcyclotetrasiloxane (TMCTS),octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS),triethoxysilane (chemical formula: SiH(OC₂H₅)₃), andtris(dimethylamino)silane (chemical formula: SiH(N(CH₃)₂)₃).

For the layer having a smooth and hydrophilic surface, silicon oxide,silicon oxynitride, silicon nitride, or silicon nitride oxide which isformed by a plasma CVD method using an inorganic silane such asmonosilane, disilane, or trisilane for a source gas can also be used.For example, a silicon nitride layer formed by a plasma CVD method usinga silane gas and an ammonia gas for a source gas can be applied. Thesource gas may further contain hydrogen. Alternatively, a siliconnitride oxide layer can be formed by a plasma CVD method using adinitrogen monoxide gas, in addition to the silane gas and the ammoniagas, for a source gas.

For example, the insulating layer 104 is formed using a stack of a50-nm-thick silicon oxynitride layer, a 50-nm-thick silicon nitrideoxide layer, and a 50-nm-thick silicon oxide layer. These insulatinglayers can be formed by a plasma CVD method. The silicon oxide layer,which is the uppermost layer and serves as the bonding plane, has an Raof 0.5 nm or less, preferably 0.3 nm or less after the formation, andthe silicon oxide layer is formed by, for example, a plasma CVD methodusing TEOS for a source gas. When the insulating layer 104 includes asilicon insulating layer containing nitrogen, specifically a siliconnitride oxide layer, diffusion of impurities from the supportingsubstrate 102 which is later bonded can be prevented.

In any case, silicon oxide, silicon nitride, silicon oxynitride, orsilicon nitride oxide formed by a CVD method such as a plasma CVDmethod, a low pressure CVD method, or an atmospheric pressure CVD methodcan be applied as long as the layer whose outermost surface is smoothcan be formed. In the case of the stacked structure, there is nolimitation on another layer except the layer which forms the outermostsurface. The insulating layer 104 needs to be formed at a temperature atwhich hydrogen is not desorbed from the fragile layer 105 formed in thesingle crystal semiconductor substrate 103, preferably at 350° C. orlower.

The surface of the single crystal semiconductor substrate 103 that isprovided with the first electrode 106 is bonded to one surface of thesupporting substrate 102 (see FIG. 4A). In this embodiment mode, theinsulating layer 104 is interposed between the first electrode 106 andthe supporting substrate 102. The bonding plane corresponds to onesurface of the insulating layer 104 (the surface not in contact with thefirst electrode 106) and the one surface of the supporting substrate102.

The bonding plane (here, the one surface of the insulating layer 104 andthe one surface of the supporting substrate 102) should be cleanedsufficiently in advance. The bonding plane is preferably cleaned bywashing or the like because a bonding defect is caused if the bondingplane has particles such as microscopic dust. Then, the insulating layer104 formed over the first electrode 106 and the supporting substrate 102are arranged in close contact, thereby forming the bonding. In thisembodiment mode, the insulating layer 104 has a hydrophilic surface andthe bonding is formed by an operation of van der Waals forces orhydrogen bonding. When one or both of the bonding planes havehydrophilic surfaces, a hydroxyl group or a water molecule functions asan adhesive and water molecules diffuse in later heat treatment. Theremaining composition forms a silanol group (Si—OH) and the bonding isformed by hydrogen bonding. Further, this bonding portion forms asiloxane bonding (O—Si—O) by release of hydrogen to become a covalentbond, which forms firmer bonding. The bonding plane of the supportingsubstrate 102 may be provided with a silicon insulating layer containingnitrogen, such as a silicon nitride layer or a silicon nitride oxidelayer. The silicon insulating layer containing nitrogen can function asa blocking layer which prevents contamination of impurities from thesupporting substrate 102.

In order to favorably perform bonding between the supporting substrate102 and the insulating layer 104, the bonding plane may be activated inadvance. For example, one or both of the bonding planes are irradiatedwith an atomic beam or an ion beam. As the atomic beam or the ion beam,an inert gas neutral atom beam or inert gas ion beam of argon or thelike can be used. It is also possible to activate the bonding plane byplasma irradiation or radical treatment. Such surface treatmentfacilitates forming of bonding between different kinds of materials evenat a temperature of 400° C. or lower. Alternatively, one or both of thebonding planes may be cleaned with ozone-containing water,oxygen-containing water, hydrogen-containing water, pure water, or thelike. Such cleaning treatment can make the bonding plane hydrophilic andincrease the number of hydroxyl groups at the bonding plane, therebyfurther strengthening the bonding.

After bonding the single crystal semiconductor substrate 103 and thesupporting substrate 102 to each other, heat treatment or pressuretreatment is preferably performed. Heat treatment or pressure treatmentcan increase the bonding strength. If the heat treatment is performed,the temperature of the heat treatment is set at a temperature that islower than or equal to the strain point of the supporting substrate 102and is a temperature which does not cause change in volume of thefragile layer 105 formed in the single crystal semiconductor substrate103, preferably at a temperature higher than or equal to roomtemperature and lower than 400° C. Note that this heat treatment andanother heat treatment for later separating part of the single crystalsemiconductor substrate using the fragile layer 105 as a separationplane may be successively performed. The pressure treatment is preformedso that pressure is applied in a direction perpendicular to the bondingplane in consideration of pressure resistance of the supportingsubstrate 102 and the single crystal semiconductor substrate 103.

If the surface of the first electrode 106 (the surface opposite to thesurface on the first impurity semiconductor layer 108 side) is smooth,specifically the average surface roughness Ra thereof is 0.5 nm or less,preferably 0.3 nm or less, bonding with the supporting substrate mightbe possible even without the insulating layer 104. In that case, thefirst electrode 106 and the supporting substrate may be directly bondedto each other without forming the insulating layer 104.

Heat treatment is performed to separate part of the single crystalsemiconductor substrate 103 from the supporting substrate 102 using thefragile layer 105 or the vicinity of the fragile layer 105 as aseparation plane. The first single crystal semiconductor layer 110separated from the single crystal semiconductor substrate 103 remainsover the supporting substrate 102, and thus a so-called SOI structure isobtained. The first single crystal semiconductor layer 110 has the sameor substantially the same crystallinity as the single crystalsemiconductor substrate 103. Moreover, a separation substrate 109 fromwhich the first single crystal semiconductor layer 110 has beenseparated is obtained (see FIG. 4B).

The temperature of the heat treatment for separating part of the singlecrystal semiconductor substrate 103 at the vicinity of the fragile layer105 is preferably higher than or equal to the temperature of forming theinsulating layer 104 and less than or equal to the strain point of thesupporting substrate 102. When the heat treatment is performed at, forexample, 400° C. or more and less than 700° C., the microvoids formed inthe fragile layer 105 change in volume, whereby separation occurs alongthe fragile layer 105. Since the insulating layer 104 is bonded to thesupporting substrate 102, the first single crystal semiconductor layer110 provided with the first electrode 106 and the first impuritysemiconductor layer 108 remains over the supporting substrate 102. Thethickness of the remaining first single crystal semiconductor layer 110almost corresponds to the depth at which the fragile layer 105 isformed, which is less than 1000 nm, preferably less than 800 nm, andmore preferably greater than or equal to 50 nm and less than or equal to300 nm.

Through the aforementioned steps, the first single crystal semiconductorlayer 110 fixed to the supporting substrate 102 can be obtained. Notethat the insulating layer 104, the first electrode 106, and the firstimpurity semiconductor layer 108 are provided between the supportingsubstrate 102 and the first single crystal semiconductor layer 110.

The separation substrate 109, i.e., the single crystal semiconductorsubstrate from which the first single crystal semiconductor layer 110has been separated can be reused after recycling process. The separationsubstrate 109 may be reused as a single crystal semiconductor substrate,which serves as a material from which a single crystal semiconductorlayer is sliced or may be used for another purpose. If the substrate isreused as a single crystal semiconductor substrate from which a singlecrystal semiconductor layer of a photoelectric conversion device isseparated, a plurality of photoelectric conversion devices can bemanufactured out of one material substrate.

An amorphous semiconductor layer 111 is formed on the first singlecrystal semiconductor layer 110 (see FIG. 5A). Note that, before theamorphous semiconductor layer 111 is formed, an oxide layer such as anatural oxide layer formed on a surface of the first single crystalsemiconductor layer 110 is removed. This is because, if the oxide layeris formed, the oxide layer is located between the first single crystalsemiconductor layer 110 and the amorphous semiconductor layer 111 tointerrupt solid phase growth in heat treatment which is performed later.The oxide layer can be removed using a solution containing fluorinatedacid. Specifically, process may be performed using fluorinated aciduntil the surface of the first single crystal semiconductor layer 110exhibits a water repellent property. The removal of the oxide layer fromthe surface of the first single crystal semiconductor layer 110 can beconfirmed by the water repellent property.

The amorphous semiconductor layer 111 may be formed using asemiconductor material that forms the first single crystal semiconductorlayer 110, and for example, an amorphous silicon layer, an amorphousgermanium layer, or the like is formed by a plasma CVD method. When thefirst single crystal semiconductor layer 110 is obtained by separating athin slice from a single crystal silicon wafer, it is preferable to forman amorphous silicon layer as the amorphous semiconductor layer 111.When the total thickness of the first single crystal semiconductor layer110 and the amorphous silicon layer is 800 nm or more, preferably, 1000nm or more and cycle time or productivity such as film formation time ora film formation cost are considered, it is preferable that theamorphous semiconductor layer 111 have a thickness of greater than orequal to 100 nm and less than or equal to 2000 nm.

As the amorphous semiconductor layer 111, an intrinsic semiconductor isformed. Alternatively, a p type amorphous semiconductor layer or an ntype amorphous semiconductor layer may be formed. Note that theorientation of the amorphous semiconductor layer 111 is disordered atthe time of film formation.

Heat treatment is performed, whereby the amorphous semiconductor layer111 is subjected to solid phase growth to form the second single crystalsemiconductor layer 112 (see FIG. 5B).

By this heat treatment, solid phase growth of the amorphoussemiconductor layer 111 whose orientation is disordered is performed,whereby single crystallization is performed to be the second singlecrystal semiconductor layer 112. In the solid phase growth of theamorphous semiconductor layer 111, the first single crystalsemiconductor layer 110 functions as a seed crystal, and singlecrystallization of the upper part of the amorphous semiconductor layer111 can be performed.

The heat treatment for the solid phase growth can be performed using aheat treatment apparatus such as a rapid thermal anneal (RTA), afurnace, a millimeter wave heating device, or the like. In addition, theheat treatment can be performed by laser beam irradiation or thermalplasma jet irradiation. A resistance heating method, a lamp heatingmethod, a gas heating method, an electromagnetic wave heating method,and the like are given as a heating method of the heat treatmentapparatus. Note that RTA is a kind of a rapid thermal processing (RTP)apparatus.

In general, a furnace is an external heating method, and the inside of achamber and a product are heated in a thermal equilibrium state. On theother hand, an RTA is used for instantaneous heating (flash heating) anddirectly gives energy to the product to heat the chamber and the productin a thermal nonequilibrium state. For the RTA apparatus, an RTA by alamp heating method (lamp rapid thermal anneal (LRTA)), an RTA by a gasheating method using a heated gas (gas rapid thermal anneal (GRTA)), anRTA by both a lamp heating method and a gas heating method, and the likeare given. An LRTA apparatus is an apparatus that heats the product byradiation of light emitted from a lamp such as a halogen lamp, a metalhalide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodiumlamp, a high pressure mercury lamp, or the like. A GRTA apparatus is anapparatus that heats a gas by heat radiation due to light emitted fromthe above-described lamp and light emitted from the lamp to heat theproduct by heat conduction from the heated gas. For the gas, an inertgas which does not react to the product by heat treatment, like a noblegas such as nitrogen, argon, or the like is used. In addition, the LRTAapparatus and the GRTA apparatus may be provided with a device thatheats the product by heat conduction or heat radiation from not only alamp but also a heater such as a resistance heater. The millimeter waveheating device is a device that heats the product by radiation ofmillimeter wave. The millimeter wave heating device may be provided witha device that heats the product by thermal conduction or heat radiationfrom a heater such as a resistance heater or the like.

When the RTA apparatus is used, it is preferable that the processtemperature be higher than or equal to 500° C. and lower than or equalto 750° C. and the process time be longer than or equal to 0.5 minutesand shorter than or equal to 3 minutes. When a furnace is used, it ispreferable that the process temperature be higher than or equal to 500°C. and lower than or equal to 600° C. and the process time be longerthan or equal to 1 hour and shorter than or equal to 4 hours.

For example, a single crystal silicon layer is applied as the firstsingle crystal semiconductor layer 110, and an amorphous silicon layerhaving a thickness of 1000 nm is formed as the amorphous semiconductorlayer 111. The RTA apparatus is used and heat treatment is performedunder conditions that the process temperature is 750° C. and the processtime is 3 minutes, whereby solid phase growth of the amorphous siliconlayer is performed and a single crystal silicon layer can be obtained.

In this manner, the amorphous semiconductor layer is formed on thesingle crystal semiconductor layer, and the solid phase growth of theformed amorphous semiconductor layer is performed, whereby the singlecrystal semiconductor layer can be formed to be thick easily. If thesingle crystal semiconductor layer is used for a photoelectricconversion layer, the photoelectric conversion efficiency can beimproved by the increase in the film thickness.

An impurity element imparting a conductivity type opposite to that ofthe first impurity semiconductor layer 108 is added through the onesurface of the second single crystal semiconductor layer 112 (thesurface which is not in contact with the first single crystalsemiconductor layer 110), whereby the second impurity semiconductorlayer 114 is formed (see FIG. 5C). The second impurity semiconductorlayer 114 is formed to have a thickness of 30 nm to 150 nm, preferably,50 nm to 100 nm. For example, phosphorus or arsenic is added as theimpurity element imparting a conductivity type opposite to that of thefirst impurity semiconductor layer 108, whereby the n type secondimpurity semiconductor layer 114 is formed. If the supporting substrate102 is a glass substrate, the substrate cannot resist processtemperature in a thermal diffusion method; therefore, the impurityelement is added by ion implantation or ion doping.

As illustrated in FIG. 13A, an amorphous semiconductor layer 113 havinga conductivity type (e.g., n type) opposite to that of the firstimpurity semiconductor layer 108 is formed on the amorphoussemiconductor layer 111. Then, heat treatment is performed to causesolid phase growth, whereby the second single crystal semiconductorlayer 112 and the second impurity semiconductor layer 114 can be formedas illustrated in FIG. 13B. An n type amorphous semiconductor layer canbe formed using silicon hydride such as silane or disilane as a sourcegas, and phosphine (PH₃) which is an n type impurity is added to thesource gas. When a p type amorphous semiconductor layer is formed,diborane (B₂H₆) may be added.

The second impurity semiconductor layer 114 as illustrated in FIG. 5Ccan be formed of an amorphous semiconductor or a microcrystalsemiconductor. Using an amorphous semiconductor or microcrystalsemiconductor for the second impurity semiconductor layer 114 does notlead to problems because a region mainly functioning as a photoelectricconversion layer is formed using the single crystal semiconductor layer.In the case of using an amorphous semiconductor or microcrystalsemiconductor for the second impurity semiconductor layer 114, thethickness is preferably small, for example 50 nm to 100 nm. This is forthe purpose of preventing recombination of carriers in the secondimpurity semiconductor layer 114.

In this manner, the unit cell 120 can be obtained in which the firstimpurity semiconductor layer 108 having one conductivity type, the firstsingle crystal semiconductor layer 110, the second single crystalsemiconductor layer 112, and the second impurity semiconductor layer 114having a conductivity type opposite to the one conductivity type aresequentially stacked.

The first impurity semiconductor layer 108, the first single crystalsemiconductor layer 110, the second single crystal semiconductor layer112, and the second impurity semiconductor layer 114 which are providedover the first electrode 106 are selectively etched to expose part ofthe first electrode 106 (preferably, an end portion of the firstelectrode 106) (see FIG. 6A).

In order to function as the photoelectric conversion device, it isnecessary to extract electric energy, which has been converted fromlight, from electrodes corresponding to a positive electrode and anegative electrode. The first electrode 106 serves as one of electrodescorresponding to a positive electrode and a negative electrode; however,the upper surface of the first electrode 106 is covered with the singlecrystal semiconductor layers and the lower surface thereof is providedwith the supporting substrate 102. Therefore, in this state, electricityis difficult to extract to the outside. Consequently, it is preferableto etch the layers over the first electrode 106 to expose part of thefirst electrode 106 and to form a leading electrode.

Specifically, a mask is formed using resist or an insulating layer suchas a silicon nitride layer over the second impurity semiconductor layer114, and etching may be performed using the mask. The etching may be dryetching with use of a fluorine based gas such as NF₃ or SF₆ under thecondition where at least the etching selectivity between the firstelectrode 106 and the layers (the first impurity semiconductor layer 108to the second impurity semiconductor layer 114) formed over the firstelectrode 106 is sufficiently high. After the etching, the mask whichhas rendered unnecessary is removed.

Although this embodiment mode describes the example in which the firstelectrode 106 is exposed after the formation of the second impuritysemiconductor layer 114, the second impurity semiconductor layer 114 canalternatively be formed after the exposure of the first electrode 106.Specifically, the second single crystal semiconductor layer 112 isformed by heat treatment, a mask is formed over the second singlecrystal semiconductor layer 112, and then etching is performed using themask to expose part of the first electrode 106. After removing the maskwhich has rendered unnecessary, an impurity element imparting aconductivity type opposite to that of the first impurity semiconductorlayer 108 is added to the second single crystal semiconductor layer 112,whereby the second impurity semiconductor layer 114 is formed.

The second electrode 118 is formed over the second impuritysemiconductor layer 114. The auxiliary electrode 116 is formed incontact with the exposed part of the first electrode 106 (see FIG. 6B).

The second electrode 118 is formed to have a grid shape (or a comb-likeshape or a pectinate shape) when seen from above, as illustrated in FIG.2. Thus, the unit cell 120 can be irradiated with light and canefficiently absorb light. There is no particular limitation on the shapeof the second electrode 118; however, it is needless to say that theeffective area where light enters expands when the area covering theunit cell 120 (the second impurity semiconductor layer 114) is made assmall as possible.

The auxiliary electrode 116 can be formed in accordance with the samesteps as those for forming the second electrode 118. In thephotoelectric conversion device of this embodiment mode, the firstelectrode 106 functions as one of electrodes corresponding to a positiveelectrode and a negative electrode. However, the first electrode 106 isformed all over the surface between the supporting substrate 102 and theunit cell 120, and thus wirings cannot be arranged freely. That's whythe auxiliary electrode 116 is formed to make it easy to extract theelectric energy which has been converted from light. The auxiliaryelectrode 116 serves as an extraction electrode.

The second electrode 118 and the auxiliary electrode 116 are each formedby a printing method or the like using aluminum, silver, lead-tin(solder), or the like. For example, the second electrode 118 and theauxiliary electrode 116 can be formed using a silver paste by a screenprinting method. In the case of forming the electrodes by a screenprinting method using paste or the like, the thickness of each electrodecan be about several micrometers to several hundreds of micrometers.However, illustrated is the schematic diagram which does not necessarilyillustrate in the actual dimension.

Thus, the photoelectric conversion device 100 can be manufactured.

Note that a passivation layer 119 which also functions as ananti-reflection layer is preferably formed over the unit cell 120 (seeFIG. 8).

It is said that a semiconductor surface generally has a reflectance of30% to 50%, though depending on wavelength. The reflection at a lightincidence surface leads to loss of incident light, which is a factor ofdecreasing photoelectric conversion efficiency. Therefore, thepassivation layer 119 whose refractive index is between the refractiveindex of air and the refractive index of a semiconductor, that is, amaterial of the light incidence surface of the unit cell 120, and whosetransmittance does not interrupt light incidence is formed over thelight incidence surface of the unit cell 120 (over the second impuritysemiconductor layer 114 in this embodiment mode). Thus, the reflectionat the incidence surface of the unit cell 120 can be prevented. As thepassivation layer 119, a silicon nitride layer, a silicon nitride oxidelayer, a magnesium fluoride layer, or the like can be used.

The passivation layer 119 is provided between the unit cell 120 and thesecond electrode 118 and between the unit cell 120 and the auxiliaryelectrode 116. In this case, after the passivation layer 119 is formedover the unit cell 120, the passivation layer 119 is etched to form anopening so that part of the second impurity semiconductor layer 114 andpart of the first electrode 106 are exposed. Alternatively, thepassivation layer 119 provided with an opening can be formed by alift-off method or the like. Then, the second electrode 118 is formed bya printing method in contact with the second impurity semiconductorlayer 114 through the opening provided in the passivation layer 119. Bythe same step, the auxiliary electrode 116 is formed in contact with thefirst electrode 106 through the opening provided in the passivationlayer 119.

With the crystal solid phase growth technique applied in themanufacturing process of this embodiment mode, the single crystalsemiconductor layer with a thickness of 1000 nm or more which functionsas a photoelectric conversion layer can be obtained. By the solid phasegrowth, the amount of a single crystal semiconductor used as a materialcan be sufficient as long as the single crystal semiconductor canfunction as a seed crystal and the consumption of the single crystalsemiconductor can be therefore suppressed. In the case of an amorphoussemiconductor or a microcrystalline semiconductor, grain boundaries trapcarriers to decrease the photoelectric conversion efficiency; incontrast, a single crystal semiconductor having no grain boundariesachieves excellent photoelectric conversion efficiency and ahighly-efficient photoelectric conversion device can therefore beprovided. Further, the structural body portion that supports thephotoelectric conversion device has been conventionally formed using asingle crystal semiconductor. However, with the structure in which asingle crystal semiconductor layer sliced from a single crystalsemiconductor substrate is fixed to a supporting substrate by atechnique of bonding different kinds of materials, the consumption of asingle crystal semiconductor can be suppressed. Moreover, the singlecrystal semiconductor substrate from which the single crystalsemiconductor layer has been separated can be reused. Therefore, theresources can be effectively used.

Part (A) of FIG. 7 is a cross-sectional schematic view illustrating anexample of the unit cell 120 having the photoelectric conversion deviceof this embodiment mode. In this unit cell 120, the p+ type firstimpurity semiconductor layer 108 (the p+ layer), the p type first singlecrystal semiconductor layer 110 (the p layer), the intrinsic type (itype) second single crystal semiconductor layer 112 (the layer), and then+ type (or n type) second impurity semiconductor layer 114 (the n+layer) are sequentially arranged. The unit cell 120 includes a singlecrystal semiconductor layer with an energy gap (Eg) of about 1.1 eV.Light enters from the side of the n+ type second impurity semiconductorlayer 114 (the n+ layer).

Part (B) of FIG. 7 is an energy band diagram corresponding to the unitcell 120 of Part (A) of FIG. 7. In Part (B) of FIG. 7, Egc₁ indicatesthe energy gaps of the first single crystal semiconductor layer 110 andthe second single crystal semiconductor layer 112, which is about 1.1eV. Ec indicates the level of the lower limit of a conduction band, Evindicates the level of the upper limit of a valence band, and Efindicates Fermi level.

Of the carriers (electrons and holes) generated by light excitation,electrons flow to the n type semiconductor layer side, whereas holesflow to the p type semiconductor layer side. If a single crystal siliconlayer with an energy gap of about 1.1 eV is used as the single crystalsemiconductor layer, a thickness of at least 800 nm is necessary toabsorb sunlight because single crystal silicon is an indirect transitiontype semiconductor and its light absorption coefficient is low. In thisembodiment mode, the increase in thickness of the single crystalsemiconductor layer functioning as the photoelectric conversion layer isachieved by the solid phase growth, and the total thickness of the firstsingle crystal semiconductor layer 110 and the second single crystalsemiconductor layer 112 is at least 800 nm. Therefore, light can beabsorbed sufficiently in the photoelectric conversion layer, so that thecarrier collecting efficiency can be increased to improve photoelectricconversion efficiency.

Further, the second single crystal semiconductor layer 112 is obtainedby solid phase growing the amorphous semiconductor layer to performsingle crystallization, and the unit cell 120 has a structure having pinjunction. Accordingly, an internal electric field can be formed withwhich the carriers are drifted so that the photoelectric conversionefficiency can be improved.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 2

In this embodiment mode, an example of a method of manufacturing aphotoelectric conversion device, which is different from that inEmbodiment Mode 1, will be described. Specifically, the example of (1)about the formation order of the fragile layer 105, the first impuritysemiconductor layer 108, the first electrode 106, and the insulatinglayer 104 is described in Embodiment Mode 1; now, examples of (2) to (4)are described in this embodiment mode. Note that a manufacturing processother than the formation order of the fragile layer 105, the firstimpurity semiconductor layer 108, the first electrode 106, and theinsulating layer 104 is based on Embodiment Mode 1; therefore,description thereof is omitted.

First, the example of the aforementioned formation order (2) isdescribed with reference to FIGS. 10A to 10D.

The protection layer 107 is formed on one surface of the single crystalsemiconductor substrate 103. Then, the substrate is irradiated with ionsor cluster ions generated from a source gas containing hydrogen throughthe surface where the protection layer 107 is formed, whereby thefragile layer 105 is formed in a region at a given depth of the singlecrystal semiconductor substrate 103 (see FIG. 10A).

Next, the first impurity semiconductor layer 108 is formed at the onesurface side of the single crystal semiconductor substrate 103 by addingan impurity element imparting one conductivity type through the surfacewhere the protection layer 107 is formed (see FIG. 10B). Note that,here, since the fragile layer 105 has already been formed, the additionof the impurity element is performed by an ion implantation method or anion doping method. This is because a high temperature processingperformed in a thermal diffusion method would cause degasification ofthe fragile layer 105 or cleavage of the fragile layer 105.

The protection layer 107 is removed and the first electrode 106 isformed (see FIG. 10C), and then the insulating layer 104 is formed overthe first electrode 106 (see FIG. 10D). The manufacturing process afterthis step is based on Embodiment Mode 1, and bonding with a supportingsubstrate is performed.

By applying the formation order (2), the single crystal semiconductorsubstrate to which an impurity element is not added is irradiated withthe ions or cluster ions to form the fragile layer; thus, variation in aregion where the fragile layer is formed can be expected to be reduced.

Next, the example of the aforementioned formation order (3) is describedwith reference to FIGS. 11A to 11D.

The first electrode 106 is formed on the one surface of the singlecrystal semiconductor substrate 103 (see FIG. 11A).

The single crystal semiconductor substrate 103 is irradiated with ionsor cluster ions generated from a source gas containing hydrogen throughthe surface where the first electrode 106 is formed, whereby the fragilelayer 105 is formed in a region at a given depth of the single crystalsemiconductor substrate 103 (see FIG. 11B).

An impurity element imparting one conductivity type is added through thesurface of the single crystal semiconductor substrate 103 where thefirst electrode 106 is formed, whereby the first impurity semiconductorlayer 108 is formed on one surface side (the first electrode 106 side)of the single crystal semiconductor substrate 103 (see FIG. 11C).

The insulating layer 104 is formed over the first electrode 106 (seeFIG. 11D). The manufacturing process after this step is based onEmbodiment Mode 1, and bonding with a supporting substrate is performed.

By applying the formation order (3), the first electrode 106 functionsas a protection layer against addition of an impurity element orirradiation with ions or cluster ions; therefore, a protection layerdoes not need to be provided separately. Accordingly, the process can beshortened.

Next, the example of the aforementioned formation order (4) is describedwith reference to FIGS. 12A to 12D.

The first electrode 106 is formed on the one surface of the singlecrystal semiconductor substrate 103 (see FIG. 12A).

An impurity element imparting one conductivity type is added through thesurface of the single crystal semiconductor substrate 103 where thefirst electrode 106 is formed, whereby the first impurity semiconductorlayer 108 is formed at the one surface side (the first electrode 106side) of the single crystal semiconductor substrate 103 (see FIG. 12B).

The single crystal semiconductor substrate 103 is irradiated with ionsor cluster ions generated from a source gas containing hydrogen throughthe surface where the first electrode 106 is formed, whereby the fragilelayer 105 is formed in a region at a given depth of the single crystalsemiconductor substrate 103 (see FIG. 12C).

The insulating layer 104 is formed over the first electrode 106 (seeFIG. 12D). The manufacturing process after this step is based onEmbodiment Mode 1, and bonding with a supporting substrate is performed.

By applying the formation order (4), the first electrode 106 functionsas a protection layer against addition of an impurity element orirradiation with ions or cluster ions; therefore, a protection layerdoes not need to be provided separately. Accordingly, the process can beshortened.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 3

In this embodiment mode, an example of a method of manufacturing aphotoelectric conversion device, which is different from that inEmbodiment Mode 1, will be described.

An example of a photoelectric conversion device which is formed bydirectly bonding the first electrode 106 and the supporting substrate102 to each other is illustrated in FIG. 23. When the first electrode106 has a smooth surface, specifically, when the first electrode 106 hasa surface with an average surface roughness Ra of 0.5 nm or less,preferably, 0.3 nm or less, the first electrode 106 and the supportingsubstrate can be bonded to each other without formation of theinsulating layer 104 illustrated in FIG. 1. The first electrode 106 isformed, the surface of the first electrode 106 which serves as a bondingplane is sufficiently cleaned, and then the first electrode 106 and thesupporting substrate 102 are arranged in close contact to each other toform a bond. Needless to say, before bonding, the bonding plane of thefirst electrode 106 or the bonding plane of the supporting substrate 102may be activated. In addition, after the first electrode 106 and thesupporting substrate 102 are bonded to each other, heat treatment orpressure treatment may be performed. Since the first electrode 106having a smooth surface is formed, the insulating layer 104 does notneed to be provided separately. Accordingly, the process can beshortened. Note that, even when the first electrode 106 has the averagesurface roughness in the above range, an insulating layer that functionsas a bonding layer may be formed in order to further increase thesmoothness of the bonding plane. In addition, an insulating layer thatfunctions as a blocking layer may be formed.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 4

In this embodiment mode, an example of a method of manufacturing aphotoelectric conversion device, which is different from that inEmbodiment Mode 1, will be described.

In Embodiment Mode 1, the surface of the first single crystalsemiconductor layer 110 which is sliced from the single crystalsemiconductor substrate 103 in FIG. 4B, that is, the surface of thefirst single crystal semiconductor layer 110 serving as a separationplane has a crystal defect due to formation of the fragile layer 105 insome cases. If a single crystal semiconductor layer which forms aphotoelectric conversion layer has a defect such as a crystal defect orthe like, trapping of carriers or the like occurs, which leads todecrease in photoelectric conversion efficiency. Accordingly, if thefirst single crystal semiconductor layer 110 has a crystal defect, it ispreferable to repair or remove the crystal defect. As a method ofrepairing or removing the crystal defects, it is preferable to applylaser processing or etching treatment.

FIG. 20 illustrates an example in which laser processing is performed inorder to repair a crystal defect remaining in the first single crystalsemiconductor layer 110. The first single crystal semiconductor layer110 is irradiated with a laser beam, whereby at least the surface sideof the first single crystal semiconductor layer 110 is melted and alower part thereof in a solid-phase state is used as a seed crystal forrecrystallization of the first single crystal semiconductor layer 110 ina later cooling step to become single crystal. The crystal defect of thefirst single crystal semiconductor layer 110 can be repaired through thestep.

It is preferable that at least an irradiation region of a laser beam beheated at 250° C. to 600° C. at the time of the aforementioned laserprocessing. When the irradiation region is heated, the melting time byirradiation with a laser beam can be increased and a defect can berepaired effectively. Although a laser beam 180 melts the surface sideof the first single crystal semiconductor layer 110, the supportingsubstrate 102 is hardly heated; therefore, a substrate with low heatresistance such as a glass substrate can be used as the supportingsubstrate. In addition, if the first electrode 106 is formed of metalwith high melting point, no adverse effect is given on the first singlecrystal semiconductor layer 110 even when heating is performed at theaforementioned temperature. Silicide is formed at an interface betweenthe metal that forms the first electrode 106 and the first impuritysemiconductor layer 108, whereby current flows more easily. In addition,the aforementioned laser processing can also perform activation of thefirst impurity semiconductor layer 108.

An example of a laser processing apparatus which can perform theaforementioned laser processing is described with reference to FIG. 21.The laser processing apparatus is provided with a laser 510, an opticalsystem 511 by which a laser beam is condensed and extended into a narrowlinear beam, a gas jet pipe 512 which controls an atmosphere of a laserirradiation region, a gas supply portion 513 which supplies anatmosphere control gas to the gas jet pipe 512, a flow control portion514, a gas heat portion 515, a substrate stage 522 which floats andtransports an irradiated body 530 (specifically, the supportingsubstrate 102 to which the first single crystal semiconductor layer 110is fixed), a guide rail 523 which supports both ends of the substrateand transports the irradiated body 530, and a gas supply portion 516which supplies a gas for floating to the substrate stage 522.

As the laser 510, a laser whose emission wavelength is in the range fromultraviolet light to visible light is selected. The laser 510 ispreferably a pulsed ArF, KrF, or XeCl excimer laser; or a pulsed solidstate laser such as an Nd—YAG laser, an YLF laser, or the like. It ispreferable that the repetition rate be 1 MHz or less and the pulse widthbe greater than or equal to 10 nanoseconds and less than or equal to 500nanoseconds. For example, a XeCl excimer laser with a repetition rate of10 Hz to 300 Hz, with a pulse width of 25 nanoseconds, and with awavelength of 308 nm is used.

The optical system 511 condenses and extends the laser beam to form alaser beam which has a linear cross section on the surface to beirradiated. The optical system 511 which forms a linear beam includes acylindrical lens array 517, a cylindrical lens 518, a mirror 519, and adoublet cylindrical lens 520. Although depending on the size of eachlens, a linear laser beam with a length of about 100 mm to 700 mm in alongitudinal direction and about 100 μm to 500 μm in a latitudinaldirection can be delivered.

The irradiated body 530 is irradiated with the laser beam condensed intoa linear shape, through a light introducing window 521 of the gas jetpipe 512. The gas jet pipe 512 is arranged adjacent to the irradiatedbody 530. A nitrogen gas is supplied to the gas jet pipe 512 from thegas supply portion 513. The nitrogen gas jets from an opening of the gasjet pipe 512 that faces the irradiated body 530. The opening of the gasjet pipe 512 is arranged along an optical axis of the linear laser beamso that the first single crystal semiconductor layer 110 fixed to thesupporting substrate 102 which is the irradiated body 530 is irradiatedwith the laser beam 180 that enters through the light introducing window521. By the nitrogen gas that jets through the opening of the gas jetpipe 512, the irradiation region of the laser beam has a nitrogenatmosphere.

The nitrogen gas supplied to the gas jet pipe 512 is heated by the gasheat portion 515 at 250° C. to 600° C., whereby the temperature of thesurface of the irradiated body 530 that is irradiated with the laserbeam can be controlled using the heated nitrogen gas. When theirradiation region is heated in advance, the melting time by theirradiation with the laser beam can be controlled as described above.

Air or nitrogen from the gas supply portion 516 is supplied to thesubstrate stage 522 through the flow control portion 514. The gassupplied from the gas supply portion 516 jets in a direction from thetop surface of the substrate stage 522 to the bottom surface of thesupporting substrate 102 of the irradiated body 530, thereby floatingthe supporting substrate 102. The irradiated body 530 is transported insuch a manner that both ends thereof are mounted on sliders 524 thatmove along the guide rail 523, and the irradiated body 530 is sprayedwith a gas from the substrate stage 522 side so that the irradiated body530 can be transported in a floating state without a bend. In the laserprocessing apparatus of this embodiment mode, a nitrogen gas jets fromthe gas jet pipe 512 to the top surface of the supporting substrate 102of the irradiated body 530; therefore, a bend of the supportingsubstrate 102 can be prevented by being sprayed with a gas also from therear side.

The substrate stage 522 may be divided into a laser irradiation portionand its vicinity, and a region other than those. The laser irradiationportion and its vicinity of the substrate stage 522 may be sprayed witha nitrogen gas heated by the gas heating portion 515, whereby thesupporting substrate 102 can be heated.

The laser processing illustrated in FIG. 20 is effective in that adefect of the first single crystal semiconductor layer 110 is repaired.That is, in the photoelectric conversion device, carriers (electrons andholes) generated by light excitation are collected to the electrode thatis formed on the surface of the semiconductor layer and are extracted ascurrent. At this time, if there is a defect in the first single crystalsemiconductor layer 110, the defect serves as a recombination center,whereby the carriers disappear to cause deterioration of a photoelectricconversion characteristic. Thus, it is effective to repair the defect ofthe single crystal semiconductor layer by laser processing.

Unevenness may be formed on the surface of the first single crystalsemiconductor layer 110 by using a phase shift mask when laserprocessing is performed. For example, a phase shift mask is used inwhich phase arrangement of squares each 10 μm on a side is performed tohave a checkered pattern or a checkered flag pattern when seen from theabove. The phase shift mask is arranged over the first single crystalsemiconductor layer 110, and the laser beam is delivered through thephase shift mask. The energy density of the laser beam per unit area isset at 650 mJ/cm², for example. The laser beam is delivered through thephase shift mask, whereby a profile of the laser beam can be made steepand the surface can have unevenness reflecting the pattern of the phaseshift mask. In this case, the surface of the first single crystalsemiconductor layer 110 can have periodic unevenness.

Etching treatment may be performed to remove the crystal defect on thesurface of the first single crystal semiconductor layer 110. The etchingmay be performed by dry etching or wet etching. In addition, unevennesswith the average surface roughness (Ra) of 7 nm to 10 nm and maximumpeak-to-valley height (P−V) of 300 nm to 400 nm remains on the surfaceof the first single crystal semiconductor layer 110 where separation ismade, in some cases. Note that the maximum peak-to-valley height hereindicates a difference between the height of the peak and the height ofthe valley. The peak and the valley herein are obtained by expandinginto three dimensions the “peak” and the “valley” that are defined byJIS B0601. The peak can be expressed as the highest point of the peak inthe specific plane and the valley can be expressed as the lowest pointof the valley in the specific plane.

The laser processing and the etching treatment may be performed incombination. In any case, a crystal defect is removed or repaired,whereby a cause to deteriorate a photoelectric conversion characteristiccan be removed.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 5

In this embodiment mode, an example of a so-called tandem photoelectricconversion device in which a plurality of unit cells is stacked will bedescribed. In this embodiment mode, a photoelectric conversion device inwhich two unit cells are stacked is described.

FIG. 14 illustrates an example of a cross-sectional schematic diagram ofa tandem photoelectric conversion device 200 of this embodiment mode.The photoelectric conversion device 200 has a structure in which thefirst unit cell 120 and a second unit cell 230 are stacked over thesupporting substrate 102. The first electrode 106 is provided betweenthe supporting substrate 102 and the first unit cell 120, and theinsulating layer 104 is provided between the first electrode 106 and thesupporting substrate 102. In this embodiment mode, the structure andmanufacturing method of the device from the supporting substrate 102 tothe first unit cell 120 is based on Embodiment Mode 1, and descriptionthereof is omitted.

The photoelectric conversion device 200 has a structure in which lightenters from the second unit cell 230 side, and the energy gap of aphotoelectric conversion layer of the second unit cell 230 is largerthan that of the first unit cell 120. Specifically, the photoelectricconversion layer of the second unit cell 230 is formed of anon-single-crystal semiconductor layer, and the photoelectric conversionlayer of the first unit cell 120 is formed of a single crystalsemiconductor layer. The photoelectric conversion layers havingdifferent energy gaps are stacked, whereby a wavelength range of lightthat can be absorbed is increased and photoelectric conversionefficiency can be improved. In particular, the wavelengths of sunlightwidely range from a short wavelength to a long wavelength, and light ofa wide wavelength range can be efficiently absorbed by use of thestructure described in this embodiment mode. In addition, aphotoelectric conversion layer with a large energy gap is arranged onthe light incident side, whereby light with a short wavelength and along wavelength can be efficiently absorbed.

The second unit cell 230 has a stacked structure in which a thirdimpurity semiconductor layer 222 having one conductivity type, anon-single-crystal semiconductor layer 224, and a fourth impuritysemiconductor layer 226 having a conductivity type opposite to that ofthe third impurity semiconductor layer 222 are sequentially formed overthe first unit cell 120. The third impurity semiconductor layer 222 hasa conductivity type opposite to that of the second impuritysemiconductor layer 114 of the first unit cell 120 which is in contactwith the third impurity semiconductor layer 222.

Amorphous silicon is typically used for the non-single-crystalsemiconductor layer 224 of the second unit cell 230. The third impuritysemiconductor layer 222 having one conductivity type and the fourthimpurity semiconductor layer 226 having a conductivity type opposite tothe one conductivity type are each formed of an amorphous semiconductorlayer or a microcrystal semiconductor layer which contains an impurityelement having a given conductivity type. Typically, amorphous siliconor microcrystal silicon is used, and amorphous silicon carbide canalternatively be applied. When the third impurity semiconductor layer222 is of p type, the fourth impurity semiconductor layer 226 is of ntype, and it is also possible that the third impurity semiconductorlayer 222 is of n type and the fourth impurity semiconductor layer 226is of p type.

Note that, instead of an amorphous semiconductor layer, a microcrystalsemiconductor layer (typically, microcrystal silicon) can be applied tothe non-single-crystal semiconductor layer 224, but in this case, it ispreferable that a thin amorphous semiconductor layer of about severalnanometers thick be formed over the first unit cell 120 before amicrocrystal semiconductor layer is formed. This is because, when amicrocrystal semiconductor layer is directly formed on a single crystalsemiconductor layer, epitaxial growth proceeds from a single crystalsemiconductor to form a single crystal semiconductor layer in somecases. Note that the third impurity semiconductor layer 222 may beformed of a single crystal semiconductor layer; therefore, the thinamorphous semiconductor layer of about several nanometers thick may beformed over the second impurity semiconductor layer 114 or the thirdimpurity semiconductor layer 222.

The non-single-crystal semiconductor layer 224 is formed bydecomposition of a source gas containing a semiconductor material gas byelectromagnetic energy. As the semiconductor material gas, siliconhydride typified by silane or disilane is used, and a gas containingsilicon fluoride or silicon chloride can alternatively be used. Thesemiconductor material gas, or the semiconductor material gas mixed withhydrogen and/or an inert gas can be used as the source gas. Thenon-single-crystal semiconductor layer 224 can be formed using a plasmaCVD apparatus by which a high frequency power from 10 MHz to 200 MHz isapplied as electromagnetic energy by use of the source gas to form athin film. As the electromagnetic energy, instead of high frequencypower, microwave power from 1 GHz to 5 GHz, typically, 2.45 GHz may beapplied. The third impurity semiconductor layer 222 and the fourthimpurity semiconductor layer 226 are formed using a plasma CVD apparatusin a similar manner by addition of diborane as an impurity to the sourcegas when a p type amorphous semiconductor layer is formed or by additionof phosphine as an impurity to the source gas when an n type amorphoussemiconductor layer is formed. Note that the non-single-crystalsemiconductor layer 224 can be formed by a sputtering method. Thenon-single-crystal semiconductor layer 224 has a thickness of greaterthan or equal to 50 nm and less than or equal to 300 nm, preferably,greater than or equal to 100 nm and less than or equal to 200 nm. Whenamorphous silicon is used as the non-single-crystal semiconductor layer224, the energy gap is 1.75 eV. With such a thickness, light in thewavelength region that is shorter than 600 nm is absorbed, wherebyphotoelectric conversion can be performed.

The first unit cell 120 is provided with the first electrode 106 on thesupporting substrate 102 side, and the second unit cell 230 is providedwith a second electrode 232 on the surface side. In addition, a firstauxiliary electrode 217 is connected to the first electrode 106, and asecond auxiliary electrode 219 is connected to the second electrode 232.The first auxiliary electrode 217 and the second auxiliary electrode 219each function as an extraction electrode (also referred to as acollector electrode) which extracts electric energy converted in thephotoelectric conversion layer. The photoelectric conversion device 200of this embodiment mode has a structure in which electrodescorresponding to a positive electrode and a negative electrode or theextraction electrodes which are connected to these are exposed to thesame surface side of the supporting substrate 102.

In this embodiment mode, the second electrode 232 is formed over theentire surface of the second unit cell 230, and the second auxiliaryelectrode 219 which is in contact with the second electrode 232 isformed in a grid shape (or a pectinate shape). The second unit cell isformed using the non-single-crystal semiconductor layer here, and thelifetime of carriers decreases; therefore, it is preferable to form thesecond electrode 232 over the entire surface of the substrate. Note thatthe second electrode 232 is formed using a transparent conductivematerial so that the unit cell absorbs light.

Next, an example of a method of manufacturing the photoelectricconversion device 200 according to this embodiment mode is describedwith reference to FIGS. 15A and 15B, and FIGS. 16A and 16B. Note that,since the manufacturing method up to the formation of the secondimpurity semiconductor layer 114 of the first unit cell 120 is based onEmbodiment Mode 1, description thereof is omitted.

The third impurity semiconductor layer 222, the non-single-crystalsemiconductor layer 224, and the fourth impurity semiconductor layer 226are sequentially formed over the first unit cell 120 (see FIG. 15A).

The third impurity semiconductor layer 222 is formed using an amorphoussemiconductor layer or microcrystal semiconductor layer having aconductivity type opposite to that of the second impurity semiconductorlayer of the first unit cell 120 that is in contact with the thirdimpurity semiconductor layer 222. Here, a p type amorphous semiconductorlayer (e.g., a p type amorphous silicon layer) or a p type microcrystalsemiconductor layer (a p type microcrystal silicon layer) is formed. Inaddition, the third impurity semiconductor layer 222 is formed to have athickness of 10 nm to 100 nm. The non-single-crystal semiconductor layer224 is formed using an intrinsic semiconductor layer (an i typeamorphous silicon layer) having a thickness of 100 nm to 300 nm,preferably, greater than or equal to 100 nm and less than or equal to200 nm. The fourth impurity semiconductor layer 226 is formed using anamorphous semiconductor layer or microcrystal semiconductor layer havinga conductivity type opposite to that of the third impurity semiconductorlayer 222. Here, an n type amorphous semiconductor layer (e.g., an ntype amorphous silicon layer) or an n type microcrystal semiconductorlayer (an n type microcrystal silicon layer) is formed. The fourthimpurity semiconductor layer 226 is formed to have a thickness of 10 nmto 100 nm.

The third impurity semiconductor layer 222, the non-single-crystalsemiconductor layer 224, and the fourth impurity semiconductor layer 226are formed by a CVD method or a sputtering method. Preferably, theselayers are formed by a plasma CVD method, and as power frequency forexcitation of plasma, high frequency power of an HF band or a VHF bandfrom 10 MHz to 200 MHz, or microwave power from 1 GHz to 5 GHz, forexample, 2.45 GHz is applied. As the source gas containing asemiconductor material gas, silicon hydride such as silane, disilane, orthe like is used, and a gas containing silicon fluoride or siliconchloride mixed with hydrogen and/or an inert gas as appropriate may beused. When a p type amorphous semiconductor layer or a p typemicrocrystal semiconductor layer is used, diborane is added to thesource gas. Meanwhile, when an n type amorphous semiconductor layer oran n type microcrystal semiconductor layer is used, phosphine is usedfor the source gas. Note that it is preferable that an impurity elementcontained in the non-single-crystal semiconductor layer 224 be reducedand oxygen and nitrogen be contained each at 1×10¹⁹/cm³ or less,preferably, 5×10¹⁸/cm³ or less.

As described above, the second unit cell 230 can be obtained in whichthe third impurity semiconductor layer 222 having one conductivity type,the non-single-crystal semiconductor layer 224, and the fourth impuritysemiconductor layer 226 having a conductivity type opposite to the oneconductivity type are sequentially stacked.

The second electrode 232 is formed over the fourth impuritysemiconductor layer 226 (see FIG. 15B). The second electrode 232 isformed using a transparent conductive material. This is because thephotoelectric conversion device 200 of this embodiment mode has astructure in which light enters from the second electrode 232 side. Asthe transparent conductive material, metal oxide such as indium tinoxide (ITO) alloy, zinc oxide, tin oxide, an alloy of indium oxide andzinc oxide, or the like is used. The second electrode 232 has athickness of 40 nm to 200 nm, preferably, 50 nm to 100 nm. In addition,the sheet resistance of the second electrode 232 may be about 20Ω/square to 200 Ω/square.

The second electrode 232 is formed by a sputtering method or a vacuumevaporation method. In this embodiment mode, it is preferable that thesecond electrode 232 be formed using a shadow mask so that the secondelectrode 232 is selectively formed in a region where the first unitcell 120 and the second unit cell 230 overlap with each other. Thesecond electrode 232 formed selectively can be used as a mask foretching to expose part (preferably an end portion) of the firstelectrode 106.

Note that, instead of the aforementioned metal oxide, a conductivemacromolecular material (also referred to as a conductive polymer) canbe used for the second electrode 232. As the conductive macromolecularmaterial, a so-called x-electron conjugated conductive macromolecule canbe used. For example, polyaniline and/or a derivative thereof,polypyrrole and/or a derivative thereof, polythiophene and/or aderivative thereof, and a copolymer of two or more of those materialscan be given.

The fourth impurity semiconductor layer 226, the non-single-crystalsemiconductor layer 224, the third impurity semiconductor layer 222, thesecond impurity semiconductor layer 114, the second single crystalsemiconductor layer 112, the first single crystal semiconductor layer110, and the first impurity semiconductor layer 108 are etched using thesecond electrode 232 as a mask to expose the part of the first electrode106 (see FIG. 16A).

The third impurity semiconductor layer 222, the non-single-crystalsemiconductor layer 224, and the fourth impurity semiconductor layer 226are formed over the entire surface of the supporting substrate 102 by aCVD method or a sputtering method. In addition, an amorphoussemiconductor layer formed by a CVD method or a sputtering method isgrown by solid phase to become a single crystal semiconductor layer, andthe second single crystal semiconductor layer 112 and the secondimpurity semiconductor layer 114 are each formed using the singlecrystal semiconductor layer over the entire surface of the supportingsubstrate 102. The electric energy converted from light in thephotoelectric conversion device is extracted from the positive electrodeand the negative electrode or from the extraction electrodes (collectorelectrodes) that are connected to the positive electrode and thenegative electrode. The first electrode 106 functions as a positiveelectrode or a negative electrode; however, as illustrated in FIG. 16A,the upper surface thereof is covered by the single crystal semiconductorlayer, and the lower surface thereof is provided with the supportingsubstrate 102. Accordingly, in this state, it is difficult to extractelectric energy from the electrode. Therefore, it is preferable that thelayers formed over the first electrode 106 be etched to expose the partof the first electrode 106 and an electrode which can serve as a leadingelectrode (in this case, the first auxiliary electrode 217) be formed.

The etching may be dry etching using a fluorine based gas such as NF₃,SF₆, or the like under the condition where the etching selectivitybetween at least the first electrode 106 and the layers formed over thefirst electrode 106 (the first impurity semiconductor layer 108 to thefourth impurity semiconductor layer 226) is sufficiently high. Since thesecond electrode 232 can be used as a mask here, a new mask for etchingis not necessary. Needless to say, a mask can be formed using resist oran insulating layer.

The first auxiliary electrode 217 which is connected to the firstelectrode 106 and the second auxiliary electrode 219 which is connectedto the second electrode 232 are formed (see FIG. 16B).

The second auxiliary electrode 219 is formed so as to have a grid shape(or a comb-like shape or a pectinate shape) as illustrated in FIG. 2when seen from above. This is because the photoelectric conversiondevice 200 of this embodiment mode has the structure in which lightenters from the second electrode 232 side and because an effective areafor light to enter the second unit cell and the first unit cell isincreased. In addition, the first auxiliary electrode 217 is formed incontact with the first electrode 106 which is exposed by the formeretching.

The first auxiliary electrode and the second auxiliary electrode may beformed using silver, lead-tin (solder), or the like by a printingmethod. For example, the first auxiliary electrode and the secondauxiliary electrode can be formed using a silver paste by a screenprinting method.

As described above, the tandem photoelectric conversion device 200 canbe formed.

Although not illustrated here, it is preferable that a passivation layerwhich also serves as an anti-reflection layer be formed for the tandemphotoelectric conversion device 200.

Here, Part (A) of FIG. 17 is a cross-sectional schematic diagramillustrating an example of the first unit cell 120 and the second unitcell 230 included in the photoelectric conversion device of thisembodiment mode. In this example, the first unit cell 120 includes thep+ type first impurity semiconductor layer 108 (the p+ layer), the ptype first single crystal semiconductor layer 110 (the p layer), theintrinsic type second single crystal semiconductor layer 112 (the ilayer), and the n+ type (or n type) second impurity semiconductor layer114 (the n+ layer); and the second unit cell 230 includes the p typethird impurity semiconductor layer 222, the intrinsic type (i type)non-single-crystal semiconductor layer 224, and the n+ type fourthimpurity semiconductor layer 226. In addition, the first unit cell 120includes a single crystal semiconductor layer having an energy gap of1.12 eV; and the second unit cell 230 includes a non-single-crystalsemiconductor layer having an energy gap of 1.75 eV. Note that lightenters from the side of the n+ type fourth impurity semiconductor layer226 (the n+ layer). Accordingly, the second unit cell 230 having anon-single-crystal semiconductor layer with a large energy gap islocated on the light incident side, and the first unit cell 120 having asingle crystal semiconductor layer with a small energy gap is arrangedat the rear thereof.

Part (B) of FIG. 17 is an energy band diagram corresponding to the firstunit cell 120 and the second unit cell 230 of Part (A) of FIG. 17. Inthe diagram, Egc₁ indicates the energy gaps of the first single crystalsemiconductor layer 110 and the second single crystal semiconductorlayer 112, which is about 1.1 eV. Egc₂ indicates the energy gap of thenon-single-crystal semiconductor layer 224, which is about 1.8 eV. Ecindicates the level of the lower limit of a conduction band, Evindicates the level of the upper limit of a valence band, and Efindicates the Fermi level.

As illustrated in the energy band diagram of Part (B) of FIG. 17,electrons of carriers generated by light excitation flow to the n typesemiconductor layer side and holes of carriers generated by lightexcitation flow to the p type semiconductor layer side. A p-n junctionis formed at a connection portion of the first unit cell 120 and thesecond unit cell 230, and a diode is inserted in a direction opposite tothe direction of current flow in terms of an equivalent circuit. In thiscase, a recombination center is formed at the bonding interface betweenthe second impurity semiconductor layer 114 and the third impuritysemiconductor layer 222, and recombination current flows at this bondinginterface. The second impurity semiconductor layer 114 is a singlecrystal semiconductor, and an amorphous semiconductor layer or amicrocrystal semiconductor layer is formed as the third impuritysemiconductor layer 222 on the second impurity semiconductor layer 114by a CVD method or a sputtering method, whereby the bonding by whichrecombination current flows at the bonding interface can be formed.

As described above, in the tandem photoelectric conversion device, whenthe first unit cell 120 having a single crystal semiconductor layer isused as a bottom cell, light of a long wavelength of 800 nm or more canbe absorbed and converted into electricity, which contributes to animprovement in photoelectric conversion efficiency. In addition, whenthe second unit cell 230 having a non-single-crystal semiconductor layeris used as a top cell, light of a short wavelength of less than 800 nmcan be absorbed and converted into electricity, which contributes to animprovement in photoelectric conversion efficiency.

In the manufacturing step according to this embodiment mode, a singlecrystal semiconductor layer having a thickness of 800 nm or more thatfunctions as a photoelectric conversion layer can be obtained byemploying a crystal solid phase growth technique. The consumption of asingle crystal semiconductor used as a raw material can be suppressed byusing solid phase growth. In addition, a single crystal semiconductorlayer is formed by slicing from a single crystal semiconductorsubstrate, and solid phase growth of an amorphous semiconductor layerformed on the single crystal semiconductor layer is performed;therefore, the single crystal semiconductor substrate after the singlecrystal semiconductor layer is separated can be reused. Accordingly,resources can be used effectively.

The photoelectric conversion device according to this embodiment modehas the structure in which the unit cells having different energy gapsare stacked, and the unit cell having a photoelectric conversion layerwith a large energy gap is arranged on the light incident side. The unitcells having different energy gaps are combined, whereby the wavelengthrange of light that is absorbed by the photoelectric conversion devicecan be extended, and sunlight that covers a wide wavelength range can beefficiently absorbed. Accordingly, the photoelectric conversioncharacteristics can be improved.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 6

In this embodiment mode, a photoelectric conversion device in which aplurality of unit cells is stacked, specifically, a so-called stackedphotoelectric conversion device 300 in which three unit cells arestacked is described.

FIG. 18 is a cross-sectional schematic diagram of an example of thestacked photoelectric conversion device 300 in which three unit cellsare stacked. The photoelectric conversion device 300 has a structure inwhich the first unit cell 120 using a single crystal semiconductor layeras a photoelectric conversion layer, the second unit cell 230 using anon-single-crystal semiconductor layer as a photoelectric conversionlayer, and a third unit cell 340 using a non-single-crystalsemiconductor layer as a photoelectric conversion layer are sequentiallystacked over the supporting substrate 102. The first electrode 106 isprovided between the supporting substrate 102 and the first unit cell120, and the insulating layer 104 is provided between the firstelectrode 106 and the supporting substrate 102. In addition, a firstauxiliary electrode 353 is selectively provided in contact with thefirst electrode 106. A second electrode 352 is provided over the thirdunit cell 340, and a second auxiliary electrode 354 is selectivelyprovided in contact with the second electrode 352.

The photoelectric conversion device 300 preferably has a structure inwhich light enters from the third unit cell 340 side, and it ispreferable to arrange the photoelectric conversion layers so that energygaps of the photoelectric conversion layers are arranged in descendingorder from the third unit cell 340 side. For example, when the firstsingle crystal semiconductor layer 110 and the second single crystalsemiconductor layer 112 of the first unit cell 120 are formed of singlecrystal silicon having an energy gap of 1.12 eV, the non-single-crystalsemiconductor layer 224 of the second unit cell 230 located closer tothe light incident side than the first unit cell 120 preferably has anenergy gap larger than 1.12 eV, and a non-single-crystal semiconductorlayer 344 of the third unit cell 340 located further closer to the lightincident side preferably has the largest energy gap. The unit cells havedifferent energy gaps and are arranged so that the energy gaps arearranged in descending order from the light incident side, whereby theunit cells can absorb light with different wavelength ranges andsunlight can be absorbed efficiently.

Amorphous silicon germanium or the like is used for thenon-single-crystal semiconductor layer 224 of the second unit cell 230to have an energy gap of 1.45 eV to 1.65 eV as described above. Inaddition, amorphous silicon or amorphous silicon carbide is used for thenon-single-crystal semiconductor layer 344 of the third unit cell 340 tohave an energy gap of 1.7 eV to 2.0 eV.

The structure and manufacturing method of the device from the supportingsubstrate 102 to the second unit cell 230 is based on Embodiment Modes 1to 5, and description thereof is omitted or simplified.

After formation up to the first unit cell 120 is performed, the thirdimpurity semiconductor layer 222, the non-single-crystal semiconductorlayer 224, and the fourth impurity semiconductor layer 226 which formthe second unit cell 230 are formed. Then, a fifth impuritysemiconductor layer 342 having one conductivity type, thenon-single-crystal semiconductor layer 344, and a sixth impuritysemiconductor layer 346 having a conductivity type opposite to the oneconductivity type are formed over the second unit cell 230, therebyforming the third unit cell 340. The fifth impurity semiconductor layer342 has a conductivity type which is opposite to that of the fourthimpurity semiconductor layer 226 of the second unit cell 230 that is incontact with the fifth impurity semiconductor layer 342.

The fifth impurity semiconductor layer 342 of the third unit cell 340 issimilar to the third impurity semiconductor layer 222 of the second unitcell 230, and the sixth impurity semiconductor layer 346 is similar tothe fourth impurity semiconductor layer 226. That is, when the fifthimpurity semiconductor layer 342 is of p type, the sixth impuritysemiconductor layer 346 is of n type, whereas when the fifth impuritysemiconductor layer 342 can be of n type, the sixth impuritysemiconductor layer 346 can be of p type. When a p type impuritysemiconductor layer is used, diborane may be added to a source gas,whereas when an n type impurity semiconductor layer is used, phosphinemay be added to a source gas.

Here, Part (A) of FIG. 19 is a cross-sectional schematic diagramillustrating an example of the first unit cell 120, the second unit cell230, and the third unit cell 340 included in the photoelectricconversion device of this embodiment mode. In this example, the firstunit cell 120 includes the p+ type first impurity semiconductor layer108 (the p+ layer), the p type first single crystal semiconductor layer110 (the p layer), the intrinsic type (i type) second single crystalsemiconductor layer 112 (the i layer), and the n+ type (or n type)second impurity semiconductor layer 114 (the n+ layer). In this example,the second unit cell 230 includes the p type third impuritysemiconductor layer 222, the intrinsic type (i type) non-single-crystalsemiconductor layer 224, and the n type fourth impurity semiconductorlayer 226. In this example, the third unit cell 340 includes the p typefifth impurity semiconductor layer 342, the intrinsic type (i type)non-single-crystal semiconductor layer 344 (the i layer), and the n+type (or n type) sixth impurity semiconductor layer 346 (the n+ layer).

Part (B) of FIG. 19 is an energy band diagram corresponding to the firstunit cell 120, the second unit cell 230, and the third unit cell of Part(A) of FIG. 19. In the diagram, Egc₁ indicates energy gaps of the firstsingle crystal semiconductor layer 110 and the second single crystalsemiconductor layer 112, Egc₂′ indicates an energy gap of thenon-single-crystal semiconductor layer 224, and Egc₃ indicates an energygap of the non-single-crystal semiconductor layer 344. In addition, Ecindicates the level of the lower limit of a conduction band, Evindicates the level of the upper limit of a valence band, and Efindicates the Fermi level. In addition, the first unit cell 120 includesa single crystal semiconductor layer having an energy gap of Egc₁, thesecond unit cell 230 includes a non-single-crystal semiconductor layerhaving an energy gap of Egc₂′ which is larger than Egc₁, and the thirdunit cell 340 includes a non-single-crystal semiconductor layer havingan energy gap of Egc₃ which is larger than Egc₂′. Note that light entersfrom the side of the n+ type sixth impurity semiconductor layer 346 (then+ layer). Accordingly, the unit cells each having a photoelectricconversion layer are arranged in such a manner that their energy gapsare arranged in descending order from the light incident side.

As illustrated in the energy band diagram of Part (B) of FIG. 19,electrons of carriers generated by light excitation flow to the n typesemiconductor layer side and holes of carriers generated by lightexcitation flow to the p type semiconductor layer side. A p-n junctionis formed at a connection portion of the first unit cell 120 and thesecond unit cell 230, and a diode is inserted in a direction opposite tothe direction of current flow in terms of an equivalent circuit. In thiscase, a recombination center is formed at the bonding interface betweenthe second impurity semiconductor layer 114 and the third impuritysemiconductor layer 222, and recombination current flows at this bondinginterface. The second impurity semiconductor layer 114 is a singlecrystal semiconductor, and an amorphous semiconductor layer or amicrocrystal semiconductor layer is formed as the third impuritysemiconductor layer 222 on the second impurity semiconductor layer 114by a plasma CVD method or the like, whereby the bonding by whichrecombination current flows at the bonding interface can be formed. Ap-n junction is also formed at a connection portion of the second unitcell 230 and the third unit cell 340, and a diode is inserted in adirection opposite to the direction of current flow in terms of anequivalent circuit. In this case, a recombination center is formed atthe bonding interface between the fourth impurity semiconductor layer226 and the fifth impurity semiconductor layer 342, and recombinationcurrent flows at this bonding interface.

As described above, in the stacked photoelectric conversion device, thewavelength range of light that is absorbed can be extended, whichcontributes to an improvement in photoelectric conversion efficiency.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 7

A photovoltaic power generation module can be manufactured using thephotoelectric conversion device obtained by Embodiment Modes 1 to 6. Inthis embodiment mode, an example of a photovoltaic power generationmodule using the photoelectric conversion device described in EmbodimentMode 1 is illustrated in FIG. 24A. A photovoltaic power generationmodule 1028 includes the unit cell 120 provided on one surface of thesupporting substrate 102. Between the supporting substrate 102 and theunit cell 120, the insulating layer 104 and the first electrode 106 aresequentially provided from the supporting substrate 102 side. The firstelectrode 106 is connected to the auxiliary electrode 116.

The auxiliary electrode 116 is formed on the one surface side of thesupporting substrate 102 (the side where the unit cell 120 is formed)and connected to a first back surface electrode 1026 to be used for aconnector, in the end region of the supporting substrate 102. The secondelectrode 118 is formed on the one surface side of the supportingsubstrate 102 (the side where the unit cell 120 is formed) and connectedto a second back surface electrode 1027 to be used for a connector, inthe end region of the supporting substrate 102. FIG. 24B is across-sectional view along a line C-D. The auxiliary electrode 116 isconnected to the first back surface electrode 1026 through a penetrationopening of the supporting substrate 102, and the second electrode 118 isconnected to the second back surface electrode 1027 through apenetration opening of the supporting substrate 102.

In this manner, the supporting substrate 102 is provided with the unitcell 120 to form the photoelectric conversion device 100. Thus, thephotovoltaic power generation module 1028 can be made thin.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

Embodiment Mode 8

FIG. 25 illustrates an example of a photovoltaic power generation systemusing the photovoltaic power generation module 1028 described inEmbodiment Mode 7. The output power of one or a plurality ofphotovoltaic power generation modules 1028 charges a battery 1030 usinga charge control circuit 1029. When the amount of charge in the battery1030 is large, the output power is output directly to a load 1031 insome cases.

When an electric double layer capacitor is used as the battery 1030, thebattery 1030 can be charged quickly without the need for chemicalreaction in charging. In addition, compared with a lead storage batteryor the like which uses chemical reaction, lifetime can be increased byabout eight times and charging and discharging efficiency can beincreased by 1.5 times. As the load 1031, lighting such as a fluorescentlamp, a light-emitting diode, or an electroluminescence panel; a smallelectronic device; and the like are given. In this way, a photovoltaicpower generation module using the photoelectric conversion device of thepresent invention can be used for various applications.

Note that this embodiment mode can be combined with any of the otherembodiment modes, as appropriate.

This application is based on Japanese Patent Application serial no.2007-310341 filed with Japan Patent Office on Nov. 30, 2007, the entirecontents of which are hereby incorporated by reference.

1. A method of manufacturing a photoelectric conversion device,comprising the steps of: providing a single crystal semiconductorsubstrate wherein the single crystal semiconductor substrate includes afragile layer in a region at a depth of less than 1000 nm from onesurface thereof and a first impurity semiconductor layer at the onesurface side thereof and the single crystal semiconductor substrate isprovided with a first electrode on the one surface side thereof; bondingthe first electrode and a supporting substrate to each other; separatingthe single crystal semiconductor substrate using the fragile layer orvicinity of the fragile layer as a separation plane so that a firstsingle crystal semiconductor layer is formed over the supportingsubstrate; forming an amorphous semiconductor layer on the first singlecrystal semiconductor layer wherein the first single crystalsemiconductor layer is located between the amorphous semiconductor layerand the first electrode; performing heat treatment for solid phasegrowth of the amorphous semiconductor layer so that a second singlecrystal semiconductor layer is formed; forming a second impuritysemiconductor layer having a conductivity type opposite to aconductivity type of the first impurity semiconductor layer at a surfaceside of the second single crystal semiconductor layer; and forming asecond electrode over the second impurity semiconductor layer.
 2. Themethod of manufacturing a photoelectric conversion device, according toclaim 1, wherein an insulating layer is formed over the first electrode,and the first electrode and the supporting substrate are bonded to eachother with the insulating layer interposed therebetween.
 3. The methodof manufacturing a photoelectric conversion device, according to claim1, wherein the fragile layer is formed by irradiating the single crystalsemiconductor substrate with ions or cluster ions generated from asource gas containing hydrogen.
 4. The method of manufacturing aphotoelectric conversion device, according to claim 3, wherein thesingle crystal semiconductor substrate is irradiated with the ions orcluster ions in such a manner that the ions or cluster ions which aregenerated are accelerated by voltage without mass separation.
 5. Themethod of manufacturing a photoelectric conversion device, according toclaim 3, wherein the ions or cluster ions contain a larger proportion ofH₃ ⁺ ions with respect to total amount of the ions or cluster ions withwhich irradiation is performed.
 6. The method of manufacturing aphotoelectric conversion device, according to claim 1, wherein a totalthickness of the first single crystal semiconductor layer and the secondsingle crystal semiconductor layer is 800 nm or more.
 7. The method ofmanufacturing a photoelectric conversion device, according to claim 1,wherein the first single crystal semiconductor layer is formed to be ofp type by using a p type single crystal semiconductor substrate as thesingle crystal semiconductor substrate, and wherein the second singlecrystal semiconductor layer is formed to be intrinsic by using anintrinsic semiconductor as the amorphous semiconductor layer.
 8. Themethod of manufacturing a photoelectric conversion device, according toclaim 7, wherein the first impurity semiconductor layer is of p typewhile the second impurity semiconductor layer is of n type.
 9. Themethod of manufacturing a photoelectric conversion device, according toclaim 1, wherein the first impurity semiconductor layer is formed at theone surface side of the single crystal semiconductor substrate by addingan impurity element imparting one conductivity type to the singlecrystal semiconductor substrate.
 10. A method of manufacturing aphotoelectric conversion device, comprising the steps of: providing asingle crystal semiconductor substrate wherein the single crystalsemiconductor substrate includes a fragile layer in a region at a depthof less than 1000 nm from one surface thereof and a first impuritysemiconductor layer at the one surface side thereof and the singlecrystal semiconductor substrate is provided with a first electrode onthe one surface side thereof; bonding the first electrode and asupporting substrate to each other; separating the single crystalsemiconductor substrate using the fragile layer or vicinity of thefragile layer as a separation plane so that a first single crystalsemiconductor layer is formed over the supporting substrate; forming afirst amorphous semiconductor layer on the first single crystalsemiconductor layer wherein the first single crystal semiconductor layeris located between the first amorphous semiconductor layer and the firstelectrode; forming a second amorphous semiconductor layer having aconductivity type opposite to a conductivity type of the first impuritysemiconductor layer on the first amorphous semiconductor layer;performing heat treatment for solid phase growth of the first amorphoussemiconductor layer and the second amorphous semiconductor layer so thata second single crystal semiconductor layer and a second impuritysemiconductor layer are formed; and forming a second electrode over thesecond impurity semiconductor layer.
 11. The method of manufacturing aphotoelectric conversion device, according to claim 10, wherein aninsulating layer is formed over the first electrode, and the firstelectrode and the supporting substrate are bonded to each other with theinsulating layer interposed therebetween.
 12. The method ofmanufacturing a photoelectric conversion device, according to claim 10,wherein the fragile layer is formed by irradiating the single crystalsemiconductor substrate with ions or cluster ions generated from asource gas containing hydrogen.
 13. The method of manufacturing aphotoelectric conversion device, according to claim 12, wherein thesingle crystal semiconductor substrate is irradiated with the ions orcluster ions in such a manner that the ions or cluster ions which aregenerated are accelerated by voltage without mass separation.
 14. Themethod of manufacturing a photoelectric conversion device, according toclaim 12, wherein the ions or cluster ions contain a larger proportionof H₃ ⁺ ions with respect to total amount of the ions or cluster ionswith which irradiation is performed.
 15. The method of manufacturing aphotoelectric conversion device, according to claim 10, wherein a totalthickness of the first single crystal semiconductor layer and the secondsingle crystal semiconductor layer is 800 nm or more.
 16. The method ofmanufacturing a photoelectric conversion device, according to claim 10,wherein the first single crystal semiconductor layer is formed to be ofp type by using a p type single crystal semiconductor substrate as thesingle crystal semiconductor substrate, and wherein the second singlecrystal semiconductor layer is formed to be intrinsic by using anintrinsic semiconductor as the first amorphous semiconductor layer. 17.The method of manufacturing a photoelectric conversion device, accordingto claim 16, wherein the first impurity semiconductor layer is of p typewhile the second impurity semiconductor layer is of n type.
 18. Themethod of manufacturing a photoelectric conversion device, according toclaim 10, wherein the first impurity semiconductor layer is formed atthe one surface side of the single crystal semiconductor substrate byadding an impurity element imparting one conductivity type to the singlecrystal semiconductor substrate.